This document provides an introduction to prestressed concrete bridge design. It discusses how prestressing concrete induces compression to counteract tensile stresses from loading. It describes methods of prestressing including pre-tensioning and post-tensioning. The key stages of pre-tensioning and post-tensioning are outlined. Design is based on serviceability limit states to ensure only limited tensile stresses occur under working loads. Stress limits for Class 1 and 2 members are provided. Basic theory equations for stresses at transfer and service conditions are presented. Methods for estimating prestress losses from elastic deformation, shrinkage, creep, relaxation and friction are described. The total prestress loss coefficient is explained. Magnel diagrams are introduced as a design tool to
This publication provides a concise compilation of selected rules in the Eurocode 8, together with relevant Cyprus National Annex, that relate to the design of common forms of concrete building structure in the South Europe. Rules from EN 1998-1-1 for global analysis, regularity criteria, type of analysis and verification checks are presented. Detail design rules for concrete beam, column and shear wall, from EN 1998-1-1 and EN1992-1-1 are presented. This guide covers the design of orthodox members in concrete frames. It does not cover design rules for steel frames. Certain practical limitations are given to the scope.
Concrete cover provides protection for steel reinforcement from corrosion. The minimum cover (Cmin) is determined based on factors such as structural class, exposure class, and fire resistance requirements. Cmin is then increased by an allowance for deviation (Δcdev) to determine the nominal cover. Proper concrete cover ensures bond between steel and concrete while avoiding excessive cover that can increase cracking and member weight. Spacers are also required to maintain clear cover distances during concreting.
This document provides an introduction to prestressed concrete bridge design. It discusses how prestressing concrete induces compression to counteract tensile stresses from loading. Prestressed concrete allows for longer concrete bridge spans through precasting units that are lifted into place. The document covers methods of prestressing including pre-tensioning and post-tensioning. It also summarizes design considerations like serviceability limits, stress limitations, prestress losses, and establishes basic inequalities for prestress force and section properties. Magnel diagrams are introduced as a way to determine appropriate prestress force and eccentricity values.
this presentation has animations, play it in ms powerpoint as slideshow for better understanding.
this module includes
a) Introduction
b) Advantages and types of
pre-stressing
c) Pre-stressing systems
d) Materials for pre-stressing
E) PREREQUISITE OF SOM
This document discusses the computation of parameters for designing reinforced concrete beams and one-way slabs. It outlines six assumptions made in the limit state design approach, including that plane sections remain plane after bending and concrete strain is limited to 0.0035. Three types of beams are described - rectangular, T, and L-beams. Equations of equilibrium are presented, including equations to calculate the total compression and tension forces, C and T. Parameters like the area of tension steel, effective depth, and neutral axis depth are also defined.
Prestressed concrete is concrete in which internal stresses are introduced to counteract external loads. Tendons are stretched elements that impart prestress, and anchorage devices enable the tendons to impart and maintain prestress. There are two main methods - pretensioning, where tendons are tensioned before concrete is cast, and post-tensioning, where tendons are tensioned against hardened concrete. Prestressed concrete uses high-strength materials like cement, concrete, and steel tendons or strands to achieve its compressive strength and durability advantages over reinforced concrete.
This document presents an example of analysis design of slab using ETABS. This example examines a simple single story building, which is regular in plan and elevation. It is examining and compares the calculated ultimate moment from CSI ETABS & SAFE with hand calculation. Moment coefficients were used to calculate the ultimate moment. However it is good practice that such hand analysis methods are used to verify the output of more sophisticated methods.
Also, this document contains simple procedure (step-by-step) of how to design solid slab according to Eurocode 2.The process of designing elements will not be revolutionised as a result of using Eurocode 2. Due to time constraints and knowledge, I may not be able to address the whole issues.
This publication provides a concise compilation of selected rules in the Eurocode 8, together with relevant Cyprus National Annex, that relate to the design of common forms of concrete building structure in the South Europe. Rules from EN 1998-1-1 for global analysis, regularity criteria, type of analysis and verification checks are presented. Detail design rules for concrete beam, column and shear wall, from EN 1998-1-1 and EN1992-1-1 are presented. This guide covers the design of orthodox members in concrete frames. It does not cover design rules for steel frames. Certain practical limitations are given to the scope.
Concrete cover provides protection for steel reinforcement from corrosion. The minimum cover (Cmin) is determined based on factors such as structural class, exposure class, and fire resistance requirements. Cmin is then increased by an allowance for deviation (Δcdev) to determine the nominal cover. Proper concrete cover ensures bond between steel and concrete while avoiding excessive cover that can increase cracking and member weight. Spacers are also required to maintain clear cover distances during concreting.
This document provides an introduction to prestressed concrete bridge design. It discusses how prestressing concrete induces compression to counteract tensile stresses from loading. Prestressed concrete allows for longer concrete bridge spans through precasting units that are lifted into place. The document covers methods of prestressing including pre-tensioning and post-tensioning. It also summarizes design considerations like serviceability limits, stress limitations, prestress losses, and establishes basic inequalities for prestress force and section properties. Magnel diagrams are introduced as a way to determine appropriate prestress force and eccentricity values.
this presentation has animations, play it in ms powerpoint as slideshow for better understanding.
this module includes
a) Introduction
b) Advantages and types of
pre-stressing
c) Pre-stressing systems
d) Materials for pre-stressing
E) PREREQUISITE OF SOM
This document discusses the computation of parameters for designing reinforced concrete beams and one-way slabs. It outlines six assumptions made in the limit state design approach, including that plane sections remain plane after bending and concrete strain is limited to 0.0035. Three types of beams are described - rectangular, T, and L-beams. Equations of equilibrium are presented, including equations to calculate the total compression and tension forces, C and T. Parameters like the area of tension steel, effective depth, and neutral axis depth are also defined.
Prestressed concrete is concrete in which internal stresses are introduced to counteract external loads. Tendons are stretched elements that impart prestress, and anchorage devices enable the tendons to impart and maintain prestress. There are two main methods - pretensioning, where tendons are tensioned before concrete is cast, and post-tensioning, where tendons are tensioned against hardened concrete. Prestressed concrete uses high-strength materials like cement, concrete, and steel tendons or strands to achieve its compressive strength and durability advantages over reinforced concrete.
This document presents an example of analysis design of slab using ETABS. This example examines a simple single story building, which is regular in plan and elevation. It is examining and compares the calculated ultimate moment from CSI ETABS & SAFE with hand calculation. Moment coefficients were used to calculate the ultimate moment. However it is good practice that such hand analysis methods are used to verify the output of more sophisticated methods.
Also, this document contains simple procedure (step-by-step) of how to design solid slab according to Eurocode 2.The process of designing elements will not be revolutionised as a result of using Eurocode 2. Due to time constraints and knowledge, I may not be able to address the whole issues.
This document discusses the design of compression members under uniaxial bending. It notes that columns are rarely under pure axial compression due to eccentricities from rigid frame action or accidental loading. Columns can experience uniaxial or biaxial bending based on the loading. The behavior depends on the relative magnitudes of the bending moment and axial load, which determine the position of the neutral axis. Methods for designing eccentrically loaded short columns include using equations that calculate the neutral axis position and failure mode, or using interaction diagrams that graphically show the safe ranges of moment and axial load.
Prestressed concrete is a combination of steel and concrete that uses compressive stresses applied during construction to oppose tensile stresses that occur in use. There are three main types: pre-tensioned concrete uses steel tendons tensioned before concrete is placed; bonded post-tensioned concrete uses unstressed steel placed then tensioned after curing; and unbonded post-tensioned concrete provides freedom of movement between steel and concrete. Pre-tensioned concrete requires molds that can resist internal forces and calculations to account for losses over time. Prestressed concrete provides benefits like reduced cracking and corrosion, higher strength, and more economical construction for bridges compared to steel.
This document provides design calculations for structural elements of a concrete car park structure according to BS-8110, including:
1. A one-way spanning roof slab with a span of 2.8m, designed as simply supported with 10mm main reinforcement bars at 300mm spacing and 8mm secondary bars.
2. A load distribution beam D and non-load bearing beam E, with calculations provided for beam D's dead and imposed loads.
3. Requirements include individual work submission by January 2nd, 2016 and assumptions to be clearly stated.
The document provides notes on masonry structures from a course at the University of Illinois. It discusses lateral strength and behavior of unreinforced masonry (URM) shear walls, including design criteria, failure modes, and examples. Key points include allowable stresses for flexure, shear, and axial loading; effects of perforations on stiffness and force distribution; and checking stresses in piers between openings.
This publication provides a concise compilation of selected rules in the Eurocode 8 Part 1 & 3, together with relevant Cyprus National Annex, that relate to the seismic design of common forms of concrete building structure in the South Europe. Rules from EN 1998-3 for global analysis, type of analysis and verification checks are presented. Detail design check rules for concrete beam, column and shear wall, from EN 1998-3 are also presented. This guide covers the assessment of orthodox members in concrete frames. It does not cover design rules for steel frames. Certain practical limitations are given to the scope.
Due to time constraints and knowledge, I may not be able to address the whole issues.
Please send me your suggestions for improvement. Anyone interested to share his/her knowledge or willing to contribute either totally a new section about Eurocode 8-3 or within this section is encouraged.
This document discusses the design of beams for torsion. It defines important terminology related to torsional design. It explains how torsion occurs in structures like bridges and buildings. It discusses threshold torsion and moment redistribution. It also covers torsional stresses, the torsional moment strength, and the torsional reinforcement required to resist torsional forces.
This document provides an overview of concrete shear wall design requirements according to the 1997 UBC and 2002 ACI code. It discusses the definition of shear walls, requirements for wall reinforcement, shear and flexural design, and determination of boundary zones using both a simplified approach based on load levels and a more rigorous approach using displacement and strain calculations. Details of boundary zone reinforcement are also covered.
This document provides an overview of design in reinforced concrete according to BS 8110. It discusses the basic materials used - concrete and steel reinforcement - and their properties. It describes two limit states for design: ultimate limit state considering failure, and serviceability limit state considering deflection and cracking. Key aspects of beam design are summarized, including types of beams, design for bending and shear resistance, and limiting deflection. Reinforcement detailing rules are also briefly covered.
This document provides an overview of connections and bracing configurations in structural steel construction. It defines simple connections, which are designed to be flexible, and moment connections, which are designed to be rigid or semi-rigid. Common types of simple and moment connections are described. The document also discusses braced frames, rigid frames, and combination frames that are used for lateral stability. Specific bracing configurations like X, chevron, and eccentric bracing are explained.
W.h.mosley, j.h.bungey. reinforced concrete design bookReyam AL Mousawi
This document summarizes a textbook on reinforced concrete design. It describes the textbook as setting out the principles of limit state design and its application to reinforced and prestressed concrete members and structures. The fourth edition incorporates information on a recently introduced British standard code for water-retaining structures. The authors have also made some minor revisions to other parts of the book.
This document provides an overview of reinforced concrete design principles for civil engineers and construction managers. It discusses the aim of structural design according to BS 8110, describes the properties and composite action of reinforced concrete, explains limit state design methodology, and summarizes key elements like slabs, beams, columns, walls, and foundations. The document also covers material properties, stress-strain curves, failure modes, and general procedures for slab sizing and design.
This document discusses T-beams, which are more suitable than rectangular beams in reinforced concrete. There are two types of T-beams: monolithic and isolated. It provides notations and code recommendations for T-beams from IS: 456. There are three cases for finding the depth of the neutral axis in a T-beam: when it lies in the flange, in the rib, or at the junction. An example problem is worked through to find the moment of resistance for a given T-beam section using the provided concrete and steel properties.
The document is a report on analyzing a fettuccine truss bridge model. It includes sections on precedent studies of truss bridges, testing of fettuccine material properties, designing and testing multiple bridge models, and analyzing the final bridge model. The group conducted material tests to understand fettuccine strength before designing 4 preliminary bridges and refining their design for the final bridge model, which they analyzed connections, load testing, and calculations on.
Ring or circular rafts can be used for cylindrical structures such as chimneys, silos, storage tanks, TV-towers and other structures. In this case, ring or circular raft is the best suitable foundation to the natural geometry of such structures. The design of circular rafts is quite similar to that of other rafts.
1. O documento apresenta notas de aula sobre flexão normal simples em vigas de concreto armado.
2. São estudadas seções retangulares com armaduras simples e duplas, e seções T com armadura simples, sob solicitação de flexão.
3. São introduzidos tópicos como cálculo de cargas verticais em vigas, prescrições construtivas para armaduras, e hipóteses básicas para o dimensionamento das seções.
The document provides a summary of modeling and analyzing slabs in ETABS, including:
1) Common assumptions made in slab modeling such as element type, meshing, shape, and acceptable error.
2) Steps for initial analysis including sketching expected results and comparing total loads.
3) Formulas and coefficients for calculating maximum bending moments in one-way and two-way slabs.
4) A process for designing solid slabs according to Eurocode 2 involving determining reinforcement ratios and areas.
This document summarizes the design of a single reinforced concrete corbel according to ACI 318-05. The corbel is 300mm wide and 500mm deep with 35MPa concrete and 415MPa steel reinforcement. It was designed to resist a vertical load of 370kN applied 100mm from the face of the column. The design includes checking the vertical load capacity, calculating the required shear friction and main tension reinforcement, and designing the horizontal reinforcement. The provided reinforcement of 3 No.6 bars for tension and 3 No.3 link bars at 100mm spacing was found to meet all design requirements.
The document discusses the principles and applications of prestressing in construction. It describes how prestressing uses tensioned steel strands or wires to put concrete members into compression through pre-tensioning or post-tensioning. This counters the tensile stresses experienced by concrete and allows for longer spans, reduced member depth, crack control, and cost savings. Common applications of prestressing include bridges, flyovers, buildings, parking structures, and industrial structures.
rectangular and section analysis in bending and shearqueripan
The document discusses the design of reinforced concrete beams for bending and shear. It covers the analysis of singly and doubly reinforced rectangular beam sections. Key points covered include the concept of neutral axis, under-reinforced and over-reinforced sections, design of bending reinforcement, design of shear reinforcement including link spacing, and deflection criteria. Worked examples are provided to demonstrate the design of bending and shear reinforcement for rectangular beams.
This homework involves analyzing an unpropped continuous prestressed composite slab. The student is asked to:
1) Calculate the cross-sectional properties of the composite section.
2) Calculate the effects of actions and stresses in the slab at midspan and over supports in serviceability limit states.
3) Check if the sections crack under these loads.
4) Calculate the design bending moment and bending moment resistance of the composite structure at midspan and supports in ultimate limit states.
5) Discuss when unpropped composite slabs may be advantageous over propped slabs.
The slab consists of a precast prestressed concrete slab cast continuously with a cast-in-place concrete
This document discusses the design of compression members under uniaxial bending. It notes that columns are rarely under pure axial compression due to eccentricities from rigid frame action or accidental loading. Columns can experience uniaxial or biaxial bending based on the loading. The behavior depends on the relative magnitudes of the bending moment and axial load, which determine the position of the neutral axis. Methods for designing eccentrically loaded short columns include using equations that calculate the neutral axis position and failure mode, or using interaction diagrams that graphically show the safe ranges of moment and axial load.
Prestressed concrete is a combination of steel and concrete that uses compressive stresses applied during construction to oppose tensile stresses that occur in use. There are three main types: pre-tensioned concrete uses steel tendons tensioned before concrete is placed; bonded post-tensioned concrete uses unstressed steel placed then tensioned after curing; and unbonded post-tensioned concrete provides freedom of movement between steel and concrete. Pre-tensioned concrete requires molds that can resist internal forces and calculations to account for losses over time. Prestressed concrete provides benefits like reduced cracking and corrosion, higher strength, and more economical construction for bridges compared to steel.
This document provides design calculations for structural elements of a concrete car park structure according to BS-8110, including:
1. A one-way spanning roof slab with a span of 2.8m, designed as simply supported with 10mm main reinforcement bars at 300mm spacing and 8mm secondary bars.
2. A load distribution beam D and non-load bearing beam E, with calculations provided for beam D's dead and imposed loads.
3. Requirements include individual work submission by January 2nd, 2016 and assumptions to be clearly stated.
The document provides notes on masonry structures from a course at the University of Illinois. It discusses lateral strength and behavior of unreinforced masonry (URM) shear walls, including design criteria, failure modes, and examples. Key points include allowable stresses for flexure, shear, and axial loading; effects of perforations on stiffness and force distribution; and checking stresses in piers between openings.
This publication provides a concise compilation of selected rules in the Eurocode 8 Part 1 & 3, together with relevant Cyprus National Annex, that relate to the seismic design of common forms of concrete building structure in the South Europe. Rules from EN 1998-3 for global analysis, type of analysis and verification checks are presented. Detail design check rules for concrete beam, column and shear wall, from EN 1998-3 are also presented. This guide covers the assessment of orthodox members in concrete frames. It does not cover design rules for steel frames. Certain practical limitations are given to the scope.
Due to time constraints and knowledge, I may not be able to address the whole issues.
Please send me your suggestions for improvement. Anyone interested to share his/her knowledge or willing to contribute either totally a new section about Eurocode 8-3 or within this section is encouraged.
This document discusses the design of beams for torsion. It defines important terminology related to torsional design. It explains how torsion occurs in structures like bridges and buildings. It discusses threshold torsion and moment redistribution. It also covers torsional stresses, the torsional moment strength, and the torsional reinforcement required to resist torsional forces.
This document provides an overview of concrete shear wall design requirements according to the 1997 UBC and 2002 ACI code. It discusses the definition of shear walls, requirements for wall reinforcement, shear and flexural design, and determination of boundary zones using both a simplified approach based on load levels and a more rigorous approach using displacement and strain calculations. Details of boundary zone reinforcement are also covered.
This document provides an overview of design in reinforced concrete according to BS 8110. It discusses the basic materials used - concrete and steel reinforcement - and their properties. It describes two limit states for design: ultimate limit state considering failure, and serviceability limit state considering deflection and cracking. Key aspects of beam design are summarized, including types of beams, design for bending and shear resistance, and limiting deflection. Reinforcement detailing rules are also briefly covered.
This document provides an overview of connections and bracing configurations in structural steel construction. It defines simple connections, which are designed to be flexible, and moment connections, which are designed to be rigid or semi-rigid. Common types of simple and moment connections are described. The document also discusses braced frames, rigid frames, and combination frames that are used for lateral stability. Specific bracing configurations like X, chevron, and eccentric bracing are explained.
W.h.mosley, j.h.bungey. reinforced concrete design bookReyam AL Mousawi
This document summarizes a textbook on reinforced concrete design. It describes the textbook as setting out the principles of limit state design and its application to reinforced and prestressed concrete members and structures. The fourth edition incorporates information on a recently introduced British standard code for water-retaining structures. The authors have also made some minor revisions to other parts of the book.
This document provides an overview of reinforced concrete design principles for civil engineers and construction managers. It discusses the aim of structural design according to BS 8110, describes the properties and composite action of reinforced concrete, explains limit state design methodology, and summarizes key elements like slabs, beams, columns, walls, and foundations. The document also covers material properties, stress-strain curves, failure modes, and general procedures for slab sizing and design.
This document discusses T-beams, which are more suitable than rectangular beams in reinforced concrete. There are two types of T-beams: monolithic and isolated. It provides notations and code recommendations for T-beams from IS: 456. There are three cases for finding the depth of the neutral axis in a T-beam: when it lies in the flange, in the rib, or at the junction. An example problem is worked through to find the moment of resistance for a given T-beam section using the provided concrete and steel properties.
The document is a report on analyzing a fettuccine truss bridge model. It includes sections on precedent studies of truss bridges, testing of fettuccine material properties, designing and testing multiple bridge models, and analyzing the final bridge model. The group conducted material tests to understand fettuccine strength before designing 4 preliminary bridges and refining their design for the final bridge model, which they analyzed connections, load testing, and calculations on.
Ring or circular rafts can be used for cylindrical structures such as chimneys, silos, storage tanks, TV-towers and other structures. In this case, ring or circular raft is the best suitable foundation to the natural geometry of such structures. The design of circular rafts is quite similar to that of other rafts.
1. O documento apresenta notas de aula sobre flexão normal simples em vigas de concreto armado.
2. São estudadas seções retangulares com armaduras simples e duplas, e seções T com armadura simples, sob solicitação de flexão.
3. São introduzidos tópicos como cálculo de cargas verticais em vigas, prescrições construtivas para armaduras, e hipóteses básicas para o dimensionamento das seções.
The document provides a summary of modeling and analyzing slabs in ETABS, including:
1) Common assumptions made in slab modeling such as element type, meshing, shape, and acceptable error.
2) Steps for initial analysis including sketching expected results and comparing total loads.
3) Formulas and coefficients for calculating maximum bending moments in one-way and two-way slabs.
4) A process for designing solid slabs according to Eurocode 2 involving determining reinforcement ratios and areas.
This document summarizes the design of a single reinforced concrete corbel according to ACI 318-05. The corbel is 300mm wide and 500mm deep with 35MPa concrete and 415MPa steel reinforcement. It was designed to resist a vertical load of 370kN applied 100mm from the face of the column. The design includes checking the vertical load capacity, calculating the required shear friction and main tension reinforcement, and designing the horizontal reinforcement. The provided reinforcement of 3 No.6 bars for tension and 3 No.3 link bars at 100mm spacing was found to meet all design requirements.
The document discusses the principles and applications of prestressing in construction. It describes how prestressing uses tensioned steel strands or wires to put concrete members into compression through pre-tensioning or post-tensioning. This counters the tensile stresses experienced by concrete and allows for longer spans, reduced member depth, crack control, and cost savings. Common applications of prestressing include bridges, flyovers, buildings, parking structures, and industrial structures.
rectangular and section analysis in bending and shearqueripan
The document discusses the design of reinforced concrete beams for bending and shear. It covers the analysis of singly and doubly reinforced rectangular beam sections. Key points covered include the concept of neutral axis, under-reinforced and over-reinforced sections, design of bending reinforcement, design of shear reinforcement including link spacing, and deflection criteria. Worked examples are provided to demonstrate the design of bending and shear reinforcement for rectangular beams.
This homework involves analyzing an unpropped continuous prestressed composite slab. The student is asked to:
1) Calculate the cross-sectional properties of the composite section.
2) Calculate the effects of actions and stresses in the slab at midspan and over supports in serviceability limit states.
3) Check if the sections crack under these loads.
4) Calculate the design bending moment and bending moment resistance of the composite structure at midspan and supports in ultimate limit states.
5) Discuss when unpropped composite slabs may be advantageous over propped slabs.
The slab consists of a precast prestressed concrete slab cast continuously with a cast-in-place concrete
Calulation of deflection and crack width according to is 456 2000Vikas Mehta
This document discusses the calculation of crack width in reinforced concrete flexural members. It provides information on:
1) Crack width is calculated to satisfy serviceability limits and is only relevant for Type 3 pre-stressed concrete members that crack under service loads.
2) Crack width depends on factors like amount of pre-stress, tensile stress in bars, concrete cover thickness, bar diameter and spacing, member depth and location of neutral axis, bond strength, and concrete tensile strength.
3) The method of calculation involves determining the shortest distance from the surface to a bar and using equations involving member depth, neutral axis depth, average strain at the surface level. Permissible crack widths are specified depending on exposure
This document provides the details and instructions for a homework assignment on calculating prestress losses and elongations in a post-tensioned beam. The beam has unbonded tendons with fixed couplers at a construction joint. Students are asked to:
1. Calculate the immediate losses due to friction, anchorage set, and concrete deformation for the tendons in Stage 1.
2. Draw a curve showing the prestress force over time from stressing to final conditions for a tendon in Stage 1.
3. Check that the allowable force in the construction joint is satisfied based on the anchor forces in Stage 1 and Stage 2.
The document provides the beam details, material properties, tendon
This document contains homework assignments for a course on prestressed concrete structures. It includes 5 assignments related to the design and analysis of precast pretensioned and post-tensioned beams. The first assignment involves designing a precast pretensioned beam and analyzing stresses, deflections, and tendon layout. The second compares required reinforcement for pretensioned, bonded post-tensioned, and unbonded post-tensioned beams. The third involves designing an unbonded post-tensioned T-beam. The fourth calculates prestress losses and deformations in an unbonded post-tensioned beam. The fifth assignment involves designing a precast pretensioned composite beam.
This document summarizes key concepts related to shear stresses and flexural design in prestressed concrete beams.
It discusses how prestressing increases the shear resistance of concrete sections by providing compression. The design ultimate shear resistance is calculated for both uncracked and cracked sections using equations that consider factors like prestressing steel stress and effective depth.
A three-case design procedure is outlined for providing shear reinforcement if needed. The document also covers flexural design basics like assuming a triangular stress distribution, calculating resistance moment using prestressing steel properties and depth parameters, and working through examples to determine moment capacity.
Prestress loss due to friction & anchorage take upAyaz Malik
This document provides a detailed procedure for calculating prestress loss due to anchorage take-up. Prestress Loss due to friction is also discussed in detail.
The beam section was designed with 42 prestressing strands located 130mm from the soffit. Section properties were calculated. Stress checks were performed at three stages to ensure stresses did not exceed allowable limits. A Magnel diagram showed the section satisfied design criteria with prestressing. Stirrup spacing of 150mm was chosen to resist shear. Total prestress losses were estimated at 26.67%. Deflections were calculated at various stages. A concrete slab was designed with reinforcement to span between beams.
This document compares the performance of a proposed innovative lightweight concrete filled steel tubular (CFST) truss bridge to a conventional reinforced cement concrete bridge through finite element analysis using ANSYS software. Two bridge models are created - a conventional RCC bridge and a CFST bridge. Both bridges are 15m in span and subjected to various loads. The analysis finds that the maximum deformation, normal stress, and normal strain for both bridges are within acceptable limits, with the CFST bridge performing better with lower deformation. It is concluded that the CFST bridge design suggests an alternative construction method for bridges.
The document discusses ACI reinforcement limits for flexural members, including:
- ACI 318-02 provides a unified procedure for reinforced and prestressed concrete design.
- Beams must be designed as either tension-controlled or in the transition between tension and compression-controlled to ensure sufficient under-reinforcement.
- Strength reduction factors vary between 0.81-0.90 for beams depending on reinforcement strain, with more brittle compression-controlled sections having lower factors of 0.70.
This document discusses losses in prestress that occur over time. It describes the different types of prestress losses, including immediate losses from elastic shortening, anchorage slip, and friction during tensioning, and time-dependent losses from creep, shrinkage, and relaxation. The types of losses are classified by time of occurrence and by the material responsible. Methods to calculate losses due to each factor are provided through equations accounting for properties of the steel and concrete used. An example calculation for estimating prestress losses in a pre-tensioned beam is also included.
This document discusses losses in prestressed concrete, including short-term and long-term losses. It describes the differences between pre-tensioned and post-tensioned concrete. Losses include elastic shortening, friction, anchorage slip, creep, shrinkage, and relaxation. Total losses can be 15-20% of the initial prestress. Post-tensioned concrete experiences more types of losses but lower overall losses compared to pre-tensioned concrete. Proper design and materials are needed to minimize losses in prestressed concrete.
This homework involves analyzing a composite pretensioned concrete beam with bonded tendons. The beam supports precast plank slabs and a cast-in-place concrete topping. The student is asked to:
1. Develop a calculation model for the beam considering effects of self-weight, plank slab installation, and live loads.
2. Check stresses in the beam and deflections under various load combinations to ensure compliance with design codes.
3. Draw a cross section of the beam showing the placement of tendons.
The provided document gives specifications of the beam, slabs, reinforcement, and loads to facilitate the design checks. Composite action between the beam and slabs is to be considered in the analysis
This document provides an overview of the design of steel beams. It discusses various beam types and sections, loads on beams, design considerations for restrained and unrestrained beams. For restrained beams, it covers lateral restraint requirements, section classification, shear capacity, moment capacity under low and high shear, web bearing, buckling, and deflection checks. For unrestrained beams, it discusses lateral torsional buckling, moment and buckling resistance checks. Design procedures and equations for determining effective properties and capacities are also presented.
The document discusses serviceability limit states for reinforced concrete structures according to BS8110. It summarizes that serviceability limit states ensure adequate deflection and crack width control. Simplified design rules provide deemed-to-satisfy provisions for deflection ratios and maximum 0.3mm crack widths. The document then outlines the code's design procedure for determining allowable span-to-depth ratios based on reinforcement ratios. It also discusses requirements for reinforcement detailing, spacing, and cover to control cracking.
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
This document provides details on the prestressing protocol for cantilever tendons on the Giborim Highway Bridge project. It includes specifications on concrete strength requirements before prestressing, equipment calibration, stressing records, grouting procedures, and safety. Prestressing will involve 26 tendons per cantilever using a bonded post-tensioning system. Segments will be constructed using balanced cantilever construction and prestressed in sequence as construction progresses.
The document discusses the prestressing of tendons for a 204m long highway bridge in Israel using balanced cantilever construction. It involves prestressing 26 tendons in 8 segments per cantilever using a bonded post-tensioning system. Concrete must reach a minimum strength of 35 MPa before prestressing, which also cannot occur earlier than 2.5 days after casting. Detailed elongation calculations are provided for stressing each tendon in sequential segments as construction progresses outward from the piers.
This document discusses the design of tension members according to IS 800-2007. It defines tension members as structural elements subjected to direct axial tensile loads. Tension members can fail due to gross section yielding, net section rupture, or block shear failure. The document describes various types of tension members including wires, bars, plates, structural shapes, and their behavior under tensile loads. It provides equations to calculate the design strength based on the different failure modes and discusses factors like slenderness ratio and shear lag that influence tension member design. Numerical examples are given to illustrate the design strength calculations.
This document discusses various types of losses in prestressing force that occur in pre-tensioned and post-tensioned concrete members. It defines key terms like prestressing force, pre-tensioning and post-tensioning. It explains different types of losses - elastic shortening, anchorage slip, friction, creep, shrinkage and relaxation. Methods to calculate losses in prestressing force due to elastic shortening are presented for different member types like axial and bending members. Friction loss occurring uniquely in post-tensioning is also explained.
Electric vehicle and photovoltaic advanced roles in enhancing the financial p...IJECEIAES
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2. azlanfka/utm05/mab1053 2
Introduction
In prestressed concrete, a prestress force is applied to a concrete
member and this induces an axial compression that counteracts all,
or part of, the tensile stresses set up in the member by applied
loading.
In the field of bridge engineering, the introduction of prestressed
concrete has aided the construction of long-span concrete bridges.
These often comprise precast units, lifted into position and then
tensioned against the units already in place, the process being
continued until the span is complete.
For smaller bridges, the use of simply supported precast
prestressed concrete beams has proved an economical form of
construction.
The introduction of ranges of standard beam section has simplified
the design and construction of these bridges.
3. azlanfka/utm05/mab1053 3
Methods of Prestressing
Pre-tensioning is used to describe a method of
prestressing in which the tendons are tensioned before the
concrete is placed, and the prestress is transferred to the
concrete when a suitable cube strength is reached.
Post-tensioning is a method of prestressing in which the
tendon is tensioned after the concrete has reached a
suitable strength. The tendons are anchored against the
hardened concrete immediately after prestressing.
4. azlanfka/utm05/mab1053 4
Pre-tensioning Method
Stage 1 Stage 2 Stage 3 Stage 4
Tendons and
reinforcement are
positioned in the
beam mould.
Tendons are stressed
to about 70% of their
ultimate strength.
Concrete is cast into
the beam mould and
allowed to cure to
the required initial
strength.
When the concrete
has cured the
stressing force is
released and the
tendons anchor
themselves in the
concrete.
5. azlanfka/utm05/mab1053 5
Post-tensioning Method
Stage 1 Stage 2 Stage 3 Stage 4
Cable ducts and
reinforcement are
positioned in the beam
mould. The ducts are
usually raised towards
the neutral axis at the
ends to reduce the
eccentricity of the
stressing force.
Concrete is cast
into the beam
mould and allowed
to cure to the
required initial
strength.
Tendons are
threaded through the
cable ducts and
tensioned to about
70% of their
ultimate strength.
Wedges are inserted
into the end
anchorages and the
tensioning force on
the tendons is
released. Grout is
then pumped into
the ducts to protect
the tendons.
6. azlanfka/utm05/mab1053 6
Serviceability Limit State
In contrast to reinforced concrete, the design of
prestressed concrete members is initially based upon the
flexural behaviour at working load conditions.
The ultimate strength of all members in bending, shear
and torsion is then checked, after the limit states of
serviceability have been satisfied.
The prime function of prestressing is to ensure that only
limited tensile stresses occur in the concrete under all
conditions within the working range of loads.
To satisfy the limit state of cracking it is necessary to
satisfy the stress limitations for the outermost fibres of a
section.
8. azlanfka/utm05/mab1053 8
Stress Limitation BS8110
In general the stress limitations adopted for bridges are
identical to BS8110 : Part 1: Clause 4.1.3. When
considering the serviceability limit state of cracking of
prestressed concrete members, three classifications of
structural members are given :
Class 1 : No tensile stresses;
Class 2 : Flexural tensile stresses, but no visible
cracking;
Class 3 : Flexural tensile stresses, but surface crack
widths not exceeding a maximum value (0.1mm for
members in aggressive environments and 0.2mm for all
other members)
10. azlanfka/utm05/mab1053 10
Limiting Stresses
The allowable compressive and tensile stresses for bonded Class 1
and Class 2 members at transfer and service load are provided by
BS8110 and summarised as follows :
Transfer Condition Service Condition
Compression 0.50 fci 0.33fcu
Tension :
Class 1
Class 2: Pretensioned
Postensioned
1.0 N/mm2
0.45 fci
0.36 fci
0
0.45 fcu
0.36 fcu
14. azlanfka/utm05/mab1053 14
Inequalities for Zt and Zb
Re-arranging the
above inequalities by
combining, the
expressions for Zt and
Zb can be obtained.
These two inequalities
may be used to
estimate the
preliminary section for
design.
'
min
max f
f
M
M
Z i
s
t
min
'
max f
f
M
M
Z i
s
b
15. azlanfka/utm05/mab1053 15
Inequalities for Prestress Force P
e
A
Z
M
f
Z
P
c
t
i
t
i
'
min
e
A
Z
M
f
Z
P
c
b
i
b
i
'
max
e
A
Z
M
f
Z
P
c
t
s
t
i
max
e
A
Z
M
f
Z
P
c
b
s
b
i
min
17. azlanfka/utm05/mab1053 17
Elastic deformation of concrete
(Clause 4.8.3 BS8110)
As the concrete is compressed an elastic shortening of the member
occurs. This movement is accompanied by an equal reduction in
length of the prestressing steel resulting in loss in prestress force.
For pretensioned beam, loss = mfco where
2
2
1 r
e
A
A
m
f
f
ps
c
pi
co
If the tendons are closely grouped in the tensile zone, the loss due
to elastic shortening may be found by taking fco as the stress in
concrete at the level of the centroid of the tendons.
18. azlanfka/utm05/mab1053 18
Elastic deformation of concrete
(Clause 4.8.3 BS8110)
The value of fco will vary along the member, since generally both e
and Mi will vary. In this case an average value of fco should be
assumed.
I
e
M
r
w
A
A
m
f
f i
ps
c
pi
co
2
2
1
For post-tensioned beam, loss = ½mfco where,
19. azlanfka/utm05/mab1053 19
Anchorage draw-in (Clause 4.8.6)
When cables are anchored in a post-
tensioned member, there is a ‘draw-in’ at
the wedges, which may amount to 5-
10mm for each cable depending on the
system used.
Loss in prestress force = (s/L)(Es)Aps kN
20. azlanfka/utm05/mab1053 20
Friction losses (Clause 4.9 BS8110)
In post-tensioned concrete there are four causes of
friction loss to be considered :
1) Between the cable and the end-anchorage.
2) Developed inside the jack as the cable passes through
it.
3) Caused by the unintentional variation in the duct
alignment known as ‘wobble’ of the duct. This loss is
described by a ‘wobble factor’ K which varies with the
rigidity of the duct, the frequency and the strength of
the duct supports. (Equation 58, Clause 4.9.3,
BS8110)
4) Due to curvature of the cable duct and the co-efficient
of friction μ between the cable and the duct. (Equation
59, Clause 4.9.4, BS8110)
22. azlanfka/utm05/mab1053 22
Friction losses
(Clause 4.9 BS8110)
The combined effect of curvature and wobble gives the
variation in prestress force at a distance x from the jack
as follows :
Kx
o
x e
P
P
For a parabolic cable profile since represents the
change in slope it is a linear function of x. Thus prestress
force Po from the jack decreases linearly with distance.
For a circular arc, θ= L/R is the change in slope or ‘angle
consumed’
23. azlanfka/utm05/mab1053 23
Concrete shrinkage (Clause 4.8.4)
The shrinkage strain εsh is taken as 300x10-6 for
pre-tensioned work and 200x10-6 for post-
tensioned concrete where stressing is assumed
to take place 2 – 3 weeks after concreting.
Normally, half the total shrinkage takes place in
the first month after transfer and ¾ of the total in
the first 6 months.
Loss in prestress force = εsh (Es)Aps kN
24. azlanfka/utm05/mab1053 24
Concrete creep (Clause 4.8.5)
The creep strain used for calculating creep
loss is given by : εr =(φfc)/Eci
φ = creep coefficient = 1.8 for transfer at 3
to 7 days or 1.4 for transfer after 28 days.
Loss of prestress = εr(Es) Aps kN
25. azlanfka/utm05/mab1053 25
Steel relaxation (Clause 4.8.2)
The long-term relaxation loss is specified in BS8110 as
the 1000-hour relaxation test value given by the tendon
manufacturer.
Loss of Prestress =
Relaxation factors x 1000hour test value
Table 4.6 (BS8110) (Clause 4.8.2.2 BS8110)
The creep loss may be assumed to take place at the
same time and in the same manner as the shrinkage
loss.
26. azlanfka/utm05/mab1053 26
Total Prestress Losses
If the initial prestress force applied to a member
is Pi, then the effective prestress force at
transfers is Pi, while that at service load is Pi.
The value of reflects the short-term losses
due to elastic shortening, anchorage draw-in
and friction.
Total loss coefficient accounts for the short
term and long-term time-dependent losses due
to concrete shrinkage and creep and steel
relaxation.
27. azlanfka/utm05/mab1053 27
Magnel Diagram
The relationship between
1/Pi and e are linear and if
plotted graphically, they
provide a useful means of
determining appropriate
values of Pi and e.
These diagrams were first
introduced by a Belgian
engineer, Magnel and hence
the name Magnel Diagram.
i
t
c
t
i M
f
Z
e
A
Z
P
'
min
1
i
b
c
b
i M
f
Z
e
A
Z
P
'
max
1
s
t
v
t
i M
f
Z
e
A
Z
P
max
1
s
b
c
b
i M
f
Z
e
A
Z
P
min
1
1
2
3
4
29. azlanfka/utm05/mab1053 29
Cable Zone and Cable Profile
Once the prestress force has been chosen based on the
most critical section, it is possible to find the limits of the
eccentricity e at sections elsewhere along the member.
An allowable cable zone is produced within which the
profile may take any shape.
The term ‘cable’ is used to denote the resultant of all the
individual tendons.
As long as the ‘cable’ lies within the zone, the stresses at
the different loading stages will not exceed the allowable
values, even though some of the tendons might
physically lie outside the cable zone.
30. azlanfka/utm05/mab1053 30
Cable Zone and Cable Profile
'
min
1
f
Z
M
P
A
Z
e t
i
i
c
t
c
b
i
b
i A
Z
M
f
Z
P
e
'
max
1
max
1
f
Z
M
P
A
Z
e t
s
i
c
t
c
b
s
b
i A
Z
M
f
Z
P
e
min
1
These inequalities may be used to plot
the permissible cable zone along the
beam and help to determine the profile
of the tendons.
31. azlanfka/utm05/mab1053 31
Shear in Prestressed Concrete
Beam
The shear resistance of prestressed concrete members
at the ultimate limit state is dependent on whether or not
the section in the region of greatest shear force has
cracked.
The mode of failure is different for the two cases. If the
section is uncracked in flexure, then failure in shear is
initiated by cracks which form in the webs of I or T
sections once the principal tensile strength has been
exceeded.
If the section is cracked, then failure is initiated by cracks
on the tension face of the member extending into the
compression zone, in a similar manner to the shear
mode for reinforced concrete members.
33. azlanfka/utm05/mab1053 33
Shear resistance of uncracked
sections, Vco
Equation 54 in BS8110
cp
prt
prt
v
co f
f
f
h
b
V 8
.
0
67
.
0 2
The values of Vco/bh for different concrete grades and levels of
prestress are given in Table 4.5 in BS8110.
For I and T-sections, the maximum principal tensile stresse occurs
at the juntion of the flange and the web (where the value of Ay >
0.67bh) and the equation gives a reasonable approximation to the
uncracked shear resistance if the centroid lies within the web.
If the centroid lies within the flange, the principal tensile stress at the
junction should be limited to 0.24√fcu and fcp should be 0.8 of the
prestress in the concrete at the junction.
34. azlanfka/utm05/mab1053 34
Shear resistance of cracked
sections, Vcr
Equation 55 in BS8110 gives an empirical expression
for the ultimate cracked shear resistance of beams
M
V
M
bd
v
f
f
V o
c
pu
pe
cr
55
.
0
1
cu
v
cr f
d
b
V 1
.
0
ps
i
pe
A
P
f
where
35. azlanfka/utm05/mab1053 35
Shear resistance of uncracked
sections, Vco
BS8110 Clause 4.3.8.2 requires that the maximum shear
stress at any section should under no circumstances
exceed 0.8√fcu or 5 N/mm2 whichever is less whether the
section is cracked or uncracked.
In determining this maximum stress, the reduction in web
width due to un-grouted post-tensioned ducts should be
considered. Even for grouted construction, only the
concrete plus one third of the duct width should be used
in finding the maximum shear stress.
The lateral spacing of the legs of the links across a
section should not exceed d. (See Clause 4.3.8.9 and
4.3.8.10)
36. azlanfka/utm05/mab1053 36
Shear reinforcement
If the shear resistance of a prestressed concrete member is not
sufficient, then shear reinforcement must be provided in the form of
links, similar to those used in reinforced concrete members.
BS8110 sates that, shear reinforcement is not required in cases
where the ultimate shear force at a section is less than 0.5Vc, where
Vc is based on the lesser of Vco and Vcr, or when the member is of
minor importance.
Where minimum links are provided in a member, the shear
resistance of these links is added to that of the member, Vc. The
cross-sectional area Asv, of the minimum links at a section are given
by,
Asv/sv = 0.4b/(0.87fyv)
Where b = breadth of the member (or of the rib in I or T section)
sv = spacing of links along the member
fyv = characteristic strength of shear reinforcement
37. azlanfka/utm05/mab1053 37
Shear reinforcement
The total shear resistance, Vr of a member with nominal
reinforcement is given by,
Vr = Vc +0.4d
Where d = depth to the centroid of the tendons and
longitudinal reinforcement
If the shear force at a given section exceeds the value
given by Vr in above equation, then the total shear force
in excess of Vc must be resisted by the shear
reinforcement, and the amount is then given by,
Asv/sv = (V-Vc)/(0.87fyvd)
See Clauses 4.3.8.6, 4.3.8.7 and 4.3.8.8 and Table 3.8
of BS8110.
38. azlanfka/utm05/mab1053 38
Ultimate Strength of Prestressed
Concrete
After designing a member to meet the stress limitations
for serviceability, it is necessary to check the ultimate
limit state.
The section analysis is carried out by the method of
strain compatibility in a similar manner to reinforced
concrete members.
The prestressing steel has an initial pre-strain which
must be included in the strains derived from the strain
diagram in flexure.
The analysis of sections in Class 1 and 2 members at
the serviceability limit state is carried out by treating the
section as linearly elastic and using ordinary bending
theory.
39. azlanfka/utm05/mab1053 39
Ultimate Strength of Prestressed
Concrete
Class 1 and 2 members are assumed to remain uncracked at
the service loads, justifying the use of a value of second
moment of area based on the gross-concrete section.
For Class 3 members, however, the concrete is assumed to
have cracked and the aim is to limit the crack widths to
acceptable levels depending on the degree of exposure of the
member.
The stress-strain curves for steel and concrete and the
simplified concrete stress block are given in the BS8110 to
enable ultimate-strength calculations to be carried out quickly
by hand.
Code formula (BS8110) and design charts (CP110:1972:
Part3) are also available for analyzing rectangular beams and
for T-beams where the neutral axis lies within the
compression flange.
42. azlanfka/utm05/mab1053 42
Ultimate Strength of Prestressed
Concrete
For members with unbonded tendons, the effect of unbonding
at the serviceability limit state is very small, but the behaviour
at the ultimate limit state is markedly different.
The ultimate moment of resistance of an unbonded section is
generally smaller than that for a similar bonded section.
The analysis of unbonded sections at the ultimate limit state
cannot be carried out based on the basic principles since the
strain is no longer equal to the strain in the concrete at the
same level because there is no bond between the two
materials. (Grouting of post-tensioned tendons after
tensioning is sometime not done due to cost and time-
consuming).
BS8110 formula may be used for unbonded sections with
different values for fpb and x.
43. azlanfka/utm05/mab1053 43
Ultimate Strength of Prestressed
Concrete
Equation 51 in BS8110 provides a formula for calculating
ultimate moment of resistance for rectangular section or
flanged section where the neutral axis lies in the flange.
(Check C>T and hf > 0.9x).
The values of fpb and x for such sections may be
obtained from Table 4.4 of Clause 4.3.7.3 inBS8110.
Mu = fpbAps(d-0.45x) where dn = 0.45x
Where fpb = tensile stress in the tendon during failure
Aps = area of tendons in tension zone
d = effective depth to centroid for Aps
x = depth of neutral axis
44. azlanfka/utm05/mab1053 44
Ultimate Strength of Prestressed
Concrete
For unbonded tendons, the values of fpb and x may be obtained from
Equation 52 and Equation 53 in BS8110 as follows :
pu
cu
ps
pu
pe
pb f
bd
f
A
f
d
l
f
f 7
.
0
7
.
1
1
7000
d
f
f
bd
f
A
f
x
pu
pb
cu
ps
pu
47
.
2
Equation 52
Equation 53
fpe = effective design prestress in tendon after all losses
fpu = characteristic strength of tendons
l = distance between two anchorages
b= width of rectangular beam or effective width of flanged beam
45. azlanfka/utm05/mab1053 45
Deflection of Prestressed Beams
The deflection of prestressed beams is difficult to assess in
practice since it is dependent upon many variables as follows :
Elastic deflection due to prestress
Elastic deflection due to initial loading
Creep deflection under sustained stresses
Deflection due to loss of prestress
Additional deflection due to live load
The deflection due to prestress may be calculated by treating
the prestress as an equivalent normal loading. Since concrete
deforms both instantaneously under load and also with time, due
to creep, the deflections of concrete structures should be
assessed under both short-term and long-term conditions.
46. azlanfka/utm05/mab1053 46
Deflection of Prestressed Beams
Prestressed concrete members differ from reinforced concrete
ones with regard to deflections as follows :
(1) Deflections under a given load can be eliminated entirely by the
use of a suitable arrangement of prestressing.
(2) Deflections in PSC members usually occur even with no applied
load ( this is known as camber) and is generally an upwards
deflection.
The use of prestress to control deflections makes it difficult to
specify span/depth ratios for initial estimation of member size.
General rough guidelines may be given for simply supported
beams : For bridge beams carrying heavy loads, a span/depth ratio
in the range of 20-26 for Class 1 members, while for Class 2 or 3
floor or roof beams, a range of span/depth ratios is 26-30.
47. azlanfka/utm05/mab1053 47
Short-term deflections for Class
1 and 2 members
In order to determine the
deflections of simply
supported members under
prestress force only, use is
made of the fact that the
moment in the member at
any section x is equal to
Pe(x) where e(x) is the
eccentricity at that section.
The prestress moment
diagram is thus
proportional to the area
between the member
centroid and the location of
the resultant prestressing
force, as shown.
P P
-Pe
48. azlanfka/utm05/mab1053 48
Short-term deflections for Class
1 and 2 members
A simplified method of
finding the maximum
deflection of concrete
members is outlined in
BS8110 and is suitable for
Class 3 members with low
percentages of
prestressing steel.
In this case, the maximum
deflection ymax is given by
ymax = KL2/rb where L is the
effective span, 1/rb is the
curvature at midspan or at
the support for a cantilever
and K is a constant which
depends on the shape of
the bending moment
diagram.
49. azlanfka/utm05/mab1053 49
Short-term deflections for Class
1 and 2 members
An alternative method of determining deflections is given
by the code ACI318-77 which uses an effective second
moment of area :
where Ig and Icr are second moments of area of the gross
and cracked sections respectively, Mcr is the bending
moment to cause cracking at the tension face and Mmax is
the maximum bending moment in the member.
50. azlanfka/utm05/mab1053 50
Long-term deflections
Long term shrinkage and creep movements will
cause the deflections of prestressed concrete
members to increase with time.
The effects of creep may be estimated by using
a method given in BS8110 whereby an effective
modulus of elasticity Eceff is given by Ect =
Ec28/(1+φ) where Ect is the instantaneous modulus
of elasticity at the age considered and φ is the
creep coefficient.
The value of Ect may be estimated from BS8110
Part 2 , Clause 7.2
51. azlanfka/utm05/mab1053 51
Long-term deflections
Where only a proportion of the service load is
permanent, the long-term curvature of a section may be
found using the following procedure :
a) Determine the short-term curvature under the permanent
load.
b) Determine the short-term curvature under the total load.
c) Determine the long-term curvature under the permanent
load.
Total long-term curvature = curvature (c ) + curvature
(b) – curvature (a).
52. azlanfka/utm05/mab1053 52
End Block Design
There are 2 problems associated with end-block design
namely, the assessment of the bursting tensile stresses
and the compressive bearing stresses directly beneath
the bearing plate.
For post-tensioned members, the prestressing force in a
tendon is applied through the anchorages as a
concentrated force.
By St. Venant’s principle, the stress distribution in a
member is reasonably uniform away from the anchorage
but in the region of the anchorage itself the stress
distribution is complex.
53. azlanfka/utm05/mab1053 53
End Block Design
The most significant effect for design is that tensile
stresses are set up transverse to the axis of the member,
tending to split the concrete apart and reinforcement
must be provided to contain the tensile stresses.
The compressive bearing stress is controlled by the
design of the anchors and the spacing between
anchorages.
A small helix if often welded to the anchor and provide
additional precaution against poor compaction. It should
not be considered as part of the reinforcement resisting
tensile bursting stresses.
54. azlanfka/utm05/mab1053 54
Bursting forces in anchorage
zones
The end-block of a
concentrically-loaded
post-tensioned
member of
rectangular cross-
section and the
distributions of
principal tensile and
compressive
stresses within the
end block is shown
in the diagram below.
55. azlanfka/utm05/mab1053 55
Bursting forces in anchorage
zones
The actual distribution of the bursting stresses is not
uniform and complex but can be approximated to
vary as shown in the diagram. The distribution can
be further approximated by a triangle. It is
sufficiently accurate to consider the resultant of
these stresses, Fbst.
At the ultimate limit state , Fbst is assumed to act in a
region extending from 0.2yo to 2yo, where yo is half
the side of the end-block. The value of Fbst as a
proportion of Pi (initial jacking force) may be found
from Table 4.7 BS8110. Fbst depends on the ratio of
ypo/yo where ypo is half the side of the loaded area.
57. azlanfka/utm05/mab1053 57
Bursting forces in anchorage
zones
Circular loaded areas should be considered as
square areas of equivalent cross-sectional area.
For post-tensioned members with bonded
tendons (i.e. grouted after tensioning) the
bursting force Fbst will be distributed in a region
extending from 0.2yo to 2yo from the loaded face
and should be resisted by reinforcement in the
form of spirals or closed links, uniformly
distributed throughout this region, and acting at
a stress of 200 N/mm2.
58. azlanfka/utm05/mab1053 58
Bursting forces in anchorage
zones
For members with unbonded tendons Fbst should
be assessed from Table 4.7 on the basis of the
characteristic tendon force; the reinforcement
provided to sustain this force may be assumed
to be acting at its design strength 0.87fy.
Where an end-block contains multiple
anchorages, it should be divided into a series of
symmetrically loaded prisms and then each
prism treated as a separate end-block.
Additional reinforcement should be provided
around the whole group of anchorages to
maintain overall equilibrium.
59. azlanfka/utm05/mab1053 59
Transmission lengths in pretensioned
members
Once the tendons in a pretensioned member has been cut, the force
in them which was initially maintained by the anchorages at the end
of the pretensioning bed, is transferred suddenly to the ends of the
concrete member. However, since there is no anchorage at the end
of the member, as in the case of post-tensioning, there can be no
force in the tendon there.
Further along the tendon, the bond between the steel and the
concrete enables the force in the tendons to build up, until some
distance from the end of the member a point is reached where the
force in the tendons equals the initial prestress force.
This distance is known as transmission length (Clause 4.10
BS8110) which depends on degree of compaction of concrete; size
and type of tendon; strength of the concrete; deformation and
surface condition of the tendon. See Clause 4.10.3 in BS8110 for
the calculation of the transmission length.
60. azlanfka/utm05/mab1053 60
Composite Construction
Many applications of prestressed concrete involve the
combination of precast prestressed concrete beams and in-
situ reinforced concrete slab.
A common example is the in-situ infill between precast bridge
beams. The beams are designed to act alone under their own
weights plus the weight of the wet concrete of the slab. Once
the concrete in the slab has hardened, provided that there is
adequate horizontal shear connection between the slab and
beam, they behave as a composite section under service load.
The beam acts as permanent formwork for the slab, which
provides the compression flange of the composite section.
The section size of the beam can thus be kept to a minimum,
since a compression flange is only required at the soffit at
transfer. This leads to the use of inverted T sections.
62. azlanfka/utm05/mab1053 62
Composite Construction
The stress distribution is due to self weight of the beam with the
maximum compressive stress at the lower extreme fiber.
Once the slab is in place, the stress distribution in the beam is
modified to take account the moment due combined section self-
weight of the beam and slab, Md.
Once the concrete in the slab has hardened and the imposed load
acts on the composite section, the additional stress distribution is
determined by using ordinary bending theory but using the
composite section properties.
The final stress distribution is a superposition of the modified stress
distribution in beam and the combined section. There is a
discontinuity in the final stress distribution under service load at the
junction between the beam and slab.
The beam has an initial stress distribution before it behaves as part
of the composite section, whereas the slab only has stresses
induced in it due to the composite action.
63. azlanfka/utm05/mab1053 63
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
A post-tensioned prestressed concrete bridge deck is in
the form of a solid slab and is simply supported over a
span of 20m. It carries a service load of 10.3 kN/m2.
Assume Class 1 member with fcu = 50.6N/mm2,
fci=40N/mm2 and the short-term and long-term losses to
be 10% and 20% respectively.
e h
64. azlanfka/utm05/mab1053 64
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
Determine the allowable concrete stresses for the solid slab deck.
Determine the minimum depth of slab required.
If the depth of slab is 525mm and the maximum eccentricity of the
tendons at midspan is 75mm above the soffit, find minimum value
of the prestress force required.
Construct a Magnel Diagram for the bridge slab and find the
minimum prestress force for a tendon eccentricity of 188mm.
Determine the cable zone for the full length of the bridge deck and
a suitable cable profile.
Determine the ultimate moment of resistance of the section at
midspan with e=188mm. Assume fpu= 1770 N/mm2, fpi=1239
N/mm2, fcu=40 N/mm2. Es = 195 kN/m2 , fy = 460 N/mm2 and total
steel area per metre = 4449 mm2. Assume grouted tendons after
tensioning.
65. azlanfka/utm05/mab1053 65
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
From BS8110, for Class 1 member , the allowable
stresses for the deck are :
f’max = 0.5 fci = 20.0 N/mm2
fmax = 0.33fcu = 16.7 N/mm2
f’min = - 1.0 N/mm2
fmin = 0 N/mm2
Moments
Mi = 24h x 202/8 where h is the overall depth of the slab.
Ms = 1200h + (10.3 x 202)/8 = (1200h + 515) kNm/m
66. azlanfka/utm05/mab1053 66
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
Using the inequalities for Zt and Zb, we have
6
10
1
8
.
0
7
.
16
9
.
0
1200
8
.
0
515
1200
9
.
0
h
h
Zt
6
10
0
9
.
0
0
.
20
8
.
0
1200
8
.
0
515
1200
9
.
0
h
h
Zb
= (7.58h + 29.28) x 106 mm3/m
= (7.50h + 28.97) x 106 mm3/m
67. azlanfka/utm05/mab1053 67
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
For a rectangular section, Zt = Zb = 103 (h2/6)106
= 0.167h2 x 109 mm3/m
Thus the two equations can be formed for h as follows :
0.167h2 x 109 = 7.58h + 29.28 x 106
0.167h2 x 109 = 7.50h +28.97 x 106
Solving these two equations gives values for h of 0.442m
and 0.440m and hence the minimum depth of the slab must
be 442mm.
When estimating initial size of section using the inequalities,
it is better to use much larger depth to ensure that ultimate
limit state is satisfied. This will also ensure that the effects of
misplaced tendons during construction will be minimized.
68. azlanfka/utm05/mab1053 68
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
Finding the minimum value of prestress force.
Assuming a depth of 525mm is used for the deck slab.
Zt = Zb = 5252 x 103/6 = 45.94 x 106 mm3/m
Ac = 5.25 x 105 mm2/m e = 525/2 – 75 = 188mm
Mi = 1200 (0.525) = 630 kNm/m Ms = 630 + 515 = 1145
kNm/m
Use the inequalities for Pi to find value of prestress for a given e,
we have 4 sets of values for P as follows :
m
kN
P
m
kN
P
m
kN
P
m
kN
P
i
i
i
i
/
0
.
5195
/
3
.
4699
/
3
.
6246
/
4
.
7473
Thus the minimum value for Pi which
lies within these limits is 5195 kN/m.
69. azlanfka/utm05/mab1053 69
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
Constructing the Magnel Diagram.
108/Pi ≥ 0.133e – 11.65
108/Pi ≥ 0.058e + 5.08
108/Pi ≤ 0.212e – 18.53
108/Pi ≤ 0.070e + 6.11
The signs of first and third inequalities have
reversed since their denominators are negative.
1
2
3
4
70. azlanfka/utm05/mab1053 70
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
By plotting the above inequalities with 108/Pi against e
then each linear relationship will define a feasible region
in which the combination of P& e may lie without
exceeding the limiting stresses.
For any given eccentricity, we can see which pair of
inequalities will give the limits for Pi. Thus for e = 188mm,
the range of allowable values for Pi is given by
inequalities (2) and (4), i.e.
From inequality (2) Pi 6246.3 kN/m
From inequality (4) Pi 5195.0 kN/m
72. azlanfka/utm05/mab1053 72
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
The limits for the cable zone are given by the
relevant inequalities :
73. azlanfka/utm05/mab1053 73
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
The values of Mi, Ms and e are calculated using two inequalities
(lower and upper limits) for half span and are summarized as follows :
The width of the zone at midspan is 232-188 = 44mm which is
sufficient to allow for any accuracies in locating the tendon ducts.
However, for the chosen prestress force of 5195.0 kN/m, the limit for e
=188mm as the maximum practical eccentricity for the slab.
Thus, if the tendons are nominally fixed with e=188mm, a small
displacement upwards would bring the prestress force outside the
cable zone. In order to overcome this, the spacing of the tendons is
decreased slightly from 265mm to 250mm giving an increased
prestress force of 5512.0 kN/m.
74. azlanfka/utm05/mab1053 74
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
The limits to the cable zone at midspan are now 172mm and 224mm.
If the shape of the chosen cable profile is parabolic, then for the
midspan eccentricity of 188mm , the shape of the profile is given by :
y = (4 x 0.188/202)x(20-x)
where y is a coordinate measured from the centroid of the section
(below centroid is positive). The coordinates of the curve along the
length of the deck can be found, and these are used to fix the tendon
ducts in position during construction. These coordinates lie within the
revised cable zone based on Pi = 5512.0 kN/m.
75. azlanfka/utm05/mab1053 75
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
The stress-strain curve
for the particular grade
of steel used is as
shown followed by the
stress and strain
distributions.
The strain pe in the
prestressing steel at the
ultimate limit state due
to prestress only is
given pe = (0.8 x
1239)/(195 x 103) =
0.00508
76. azlanfka/utm05/mab1053 76
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
The total strain in the steel pb = pe + p and
p is determined from the strain diagram as
follows :
0.0035/x = p / (450 – x )
p = (450 – x ) ( 0.0035/x )
The stress in the steel is found from the stress-
strain curve and the forces in the concrete and
steel, C and T respectively, are then determined
(see table shown). The neutral axis may thus be
taken with sufficient accuracy to be 336mm,
showing that the steel has not yielded.
77. azlanfka/utm05/mab1053 77
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
The ultimate moment of resistance ,
Mult = 5440(450-0.45x336)x 10-3
= 1625.5 kNm/m
The ultimate applied uniform load = 1.4 x 12.6 + 1.6 x 10.3 = 34.1
kN/m2
The maximum ultimate bending moment, Mapplied = 34.1 x 202/8 =
1705 kNm/m
78. azlanfka/utm05/mab1053 78
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
Since Mult < Mapplied, extra untensioned reinforcement is required.
The effective depth for this extra steel is 525-50 = 475 mm.
In order to estimate the required amount of untensioned
reinforcement As, it may be assumed initially that both the
prestressing steel and the untensioned reinforcement have not
yielded.
If the neutral axis is taken as 370mm, an equilibrium equation can
be written to determine As.
0.45 x 40 x 103 x 0.9 x 370 = {[(450-370)/370] x 0.0035
+ 0.00508} x 195 x 103 x 4449
+ [(475-370)/370] x 0.0035 x 200 x 103As
As = 4683 mm2/m
This will be provided by T32 bars at 150mm centers (As = 5360
mm2/m).
79. azlanfka/utm05/mab1053 79
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
The required As = 4683 mm2/m will be provided by T32
bars at 150mm centers (As = 5360 mm2/m).
It is now necessary to check that the ultimate moment of
resistance is greater than the applied bending moment.
This is achieved by using a trial-and-error procedure and
values are summarized in the following table.
80. azlanfka/utm05/mab1053 80
Example on Post-Tensioned Concrete
Slab Bridge (Ref: M. K. Hurst)
The strain in the un-
tensioned reinforcement is
given by st = (475-
x)(0.0035/x) and the
corresponding stress fst is
found from the appropriate
stress-strain curve.
The depth of the neutral axis is 373mm and the ultimate moment of
resistance is given by,
Mult = [4449 x 1131(450-373) + 5360 x 192(475-0.45x373)] x 10-6
= 1735.8 kNm/m
Mult > Mapplied therefore the section is satisfactory.