This document is a seminar report submitted by Alok B. Rathod for his Master's degree in Civil Engineering. The report examines the effects of blast loading on reinforced concrete structures. It first provides background on blast phenomena such as shock waves and dynamic loadings. It then discusses how blasts can affect structures and methods for analyzing structural response to blast loads. The report also presents case studies on the behavior of reinforced concrete columns and panels subjected to blast loading through experiments. It concludes with recommendations for further research on improving blast resistance of structures.
Seminar on Bomb Blast Resistant Structure by Shantanu PatilShantanu Patil
The design of civilian or commercial buildings to withstand the effects of a terrorist blast is unlike the design of military installations or the design of embassy buildings. The objectives of the “Structural Engineering Guidelines” for the Design of New Embassy Buildings are to prevent heavy damage to components and structural collapse. Adherence to the provisions of the guidelines will minimize injuries and loss of life and facilitate the evacuation and rescue of survivors. The blast-protection objective of any commercial or public building must be similar to those of embassy structures, that is to prevent structural collapse, to save lives, and to evacuate victims.
As we know that in today’s world terrorists’ attacks are common and not a single country is completely safe. High-explosive detonations propagate blast energy in all directions, causing extensive damage to both the target structure and nearby buildings. Structural damage and the glass exposure have been major contributors to death and injury for the targeted buildings. If the structures are properly designed for these abnormal loads damage can be controlled. Within the Indian Standard Codes these types of situations are not dealt with and they need further explanation as the engineers have no guidelines on how to design or evaluate structures for the blast phenomenon for which a detailed understanding of structural behavior as well as effects of different kinds of blast load is required. The calculation of blast load is studied in this report using various parameters.
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.
Dhruvin Goyani
M.Tech Structural
This PPT is For All the Civil Engineering Students and Specially for M.tech Students Who Trying To Learn Something New on Earthquake and its Resisting Methods and also For Seismic Analysis
Bracing elements in structural system plays a vital role in the seismic behaviour of high rise buildings during earthquake. Many of the structural failures in buildings during strong earthquake shaking have indicated that sustainable strength and stable energy dissipation capability are most desirable to maintain inter story drifts and overall structural displacements within tolerable levels. So earthquake action brings a greater concern in the structural design of buildings which is situated in earthquake prone areas. Steel bracing are the common type which mainly used to resist the lateral loads acting during a seismic activity. Conventional types of lateral load resisting systems are concentrically-braced frames (CBFs) and eccentrically braced frames (EBF). Buckling Restrained Braces (BRB) are recent developed structural system which has a stable energy dissipation property. Main advantage of BRB is its ability to yield both in tension and compression without buckling, thus obtaining a stable hysteresis loop. The BRB brace placed in a concentric frame is termed as BRBF system.
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.
Architectural And Structural Design Of Blast Resistant Buildings - REPORTPaul Jomy
The objective of this study is to shed light on blast resistant building theories, the enhancement of building security against the effect of explosives in both architectural and structural design process and the design techniques that should be carried out. Firstly, explosives and explosion type have been explained briefly. In addition, the general aspects of explosion process have been presented to clarify the effect of explosives on buildings. To have a better understanding of explosives and characteristics of explosions will enable us to make blast resistant building design much more efficiently. Essential techniques for increasing the capacity of a building to provide protection against explosive effects is discussed both with an architectural and structural approach.
Architectural And Structural Design Of Blast Resistant Buildings - PRESENTATIONPaul Jomy
The objective of this study is to shed light on blast resistant building theories, the enhancement of building security against the effect of explosives in both architectural and structural design process and the design techniques that should be carried out. Firstly, explosives and explosion type have been explained briefly. In addition, the general aspects of explosion process have been presented to clarify the effect of explosives on buildings. To have a better understanding of explosives and characteristics of explosions will enable us to make blast resistant building design much more efficiently. Essential techniques for increasing the capacity of a building to provide protection against explosive effects is discussed both with an architectural and structural approach.
Seminar on Bomb Blast Resistant Structure by Shantanu PatilShantanu Patil
The design of civilian or commercial buildings to withstand the effects of a terrorist blast is unlike the design of military installations or the design of embassy buildings. The objectives of the “Structural Engineering Guidelines” for the Design of New Embassy Buildings are to prevent heavy damage to components and structural collapse. Adherence to the provisions of the guidelines will minimize injuries and loss of life and facilitate the evacuation and rescue of survivors. The blast-protection objective of any commercial or public building must be similar to those of embassy structures, that is to prevent structural collapse, to save lives, and to evacuate victims.
As we know that in today’s world terrorists’ attacks are common and not a single country is completely safe. High-explosive detonations propagate blast energy in all directions, causing extensive damage to both the target structure and nearby buildings. Structural damage and the glass exposure have been major contributors to death and injury for the targeted buildings. If the structures are properly designed for these abnormal loads damage can be controlled. Within the Indian Standard Codes these types of situations are not dealt with and they need further explanation as the engineers have no guidelines on how to design or evaluate structures for the blast phenomenon for which a detailed understanding of structural behavior as well as effects of different kinds of blast load is required. The calculation of blast load is studied in this report using various parameters.
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.
Dhruvin Goyani
M.Tech Structural
This PPT is For All the Civil Engineering Students and Specially for M.tech Students Who Trying To Learn Something New on Earthquake and its Resisting Methods and also For Seismic Analysis
Bracing elements in structural system plays a vital role in the seismic behaviour of high rise buildings during earthquake. Many of the structural failures in buildings during strong earthquake shaking have indicated that sustainable strength and stable energy dissipation capability are most desirable to maintain inter story drifts and overall structural displacements within tolerable levels. So earthquake action brings a greater concern in the structural design of buildings which is situated in earthquake prone areas. Steel bracing are the common type which mainly used to resist the lateral loads acting during a seismic activity. Conventional types of lateral load resisting systems are concentrically-braced frames (CBFs) and eccentrically braced frames (EBF). Buckling Restrained Braces (BRB) are recent developed structural system which has a stable energy dissipation property. Main advantage of BRB is its ability to yield both in tension and compression without buckling, thus obtaining a stable hysteresis loop. The BRB brace placed in a concentric frame is termed as BRBF system.
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.
Architectural And Structural Design Of Blast Resistant Buildings - REPORTPaul Jomy
The objective of this study is to shed light on blast resistant building theories, the enhancement of building security against the effect of explosives in both architectural and structural design process and the design techniques that should be carried out. Firstly, explosives and explosion type have been explained briefly. In addition, the general aspects of explosion process have been presented to clarify the effect of explosives on buildings. To have a better understanding of explosives and characteristics of explosions will enable us to make blast resistant building design much more efficiently. Essential techniques for increasing the capacity of a building to provide protection against explosive effects is discussed both with an architectural and structural approach.
Architectural And Structural Design Of Blast Resistant Buildings - PRESENTATIONPaul Jomy
The objective of this study is to shed light on blast resistant building theories, the enhancement of building security against the effect of explosives in both architectural and structural design process and the design techniques that should be carried out. Firstly, explosives and explosion type have been explained briefly. In addition, the general aspects of explosion process have been presented to clarify the effect of explosives on buildings. To have a better understanding of explosives and characteristics of explosions will enable us to make blast resistant building design much more efficiently. Essential techniques for increasing the capacity of a building to provide protection against explosive effects is discussed both with an architectural and structural approach.
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Architectural And Structural Design Of Blast Resistant BuildingsPaul Jomy
The objective of this study is to shed light on blast resistant building theories, the enhancement of building security against the effect of explosives in both architectural and structural design process and the design techniques that should be carried out. Firstly, explosives and explosion type have been explained briefly. In addition, the general aspects of explosion process have been presented to clarify the effect of explosives on buildings. To have a better understanding of explosives and characteristics of explosions will enable us to make blast resistant building design much more efficiently. Essential techniques for increasing the capacity of a building to provide protection against explosive effects is discussed both with an architectural and structural approach.
Study on the performance of cfrp strengthened circular hollow steel sectionseSAT Journals
Abstract Compared to conventional steel sections, the Steel Hollow Sections have better structural performance due to excellent properties of the tubular shape with regard to loading in compression, torsion and bending in all directions. In many structural engineering applications Hollow Sections are widely used such as airport terminal buildings, railway stations, industrial structures, etc. Carbon Fibre Reinforced Polymer (CFRP) strengthening of structures has been with success applied to concrete structures, and additionally it applied to steel structures recently. In hollow section, Steel-CFRP composite combine the benefits of the high strength to weight ratio and more ductile. This paper presents an experimental investigation carried out with two different matrix layouts of carbon fibres on the axial capacity and crushing behaviour of CFRP strengthened Circular Hollow Section (CHS). With and without CFRP wrapping the experiments were conducted on short steel columns. From the experimental studies It has been inferred that the application of CFRP to short column sections increases ductility of the section and also increases axial load carrying capacity of the section. To improve the performance of existing structures, Carbon fibre could also be with success externally bonded to metal CHS, and such application could also be provided. Keywords: Steel Hollow Sections, Carbon Fibre Reinforced Polymer, axial capacity, short steel columns, ductility
PERFORMANCE OF CARBON FIBER AS LATERAL TIES IN SHORT AXIALLY LOADED CONCRETE ...IAEME Publication
An experimental program to investigate the structural performance of CFRP as lateral tie in concrete column is conducted. The experimental program consist of twenty one number of column fabricated and tested experimentally under axial load. Specimens were divided into four groups and each group except group 1 consists of six columns. Group 1 consist of reference columns; three plain concrete and six specimen reinforced with steel reinforcement. Group 2 columns were reinforced with CFRP lateral tie and columns of group 3 were reinforced with CFRP lateral ties except end ties to solve fabrication issue. Size of all the columns was kept same, 600 mm in height and 150 in mm diameter. Results shows a significant increase in axial capacity of column tied with CFRP lateral ties. Column with end steel ties shows similar behaviour as CFRP tied column.
Behavior of RCC Structural Members for Blast Analysis: A ReviewIJERA Editor
In today’s scenario threat of enemies and terrorist attack is increasing. Therefore consideration of blast load in analysis and design is essential. A bomb explosion within or nearby outside the building can cause catastrophic failure of building. Blast loads have, in the recent past, become important service loads for certain categories of structure. An important task in blast resistance design is to make a realistic prediction of blast pressure. The distance of explosion from the structure is an important datum, governing the magnitude and duration of blast loads. In the present study, the RCC frame was analyzed by using conventional code for gravity loads using moment resisting frame. The blast load was calculated using UFC-340-02 (2008) or IS 4991-1968 for 500 kg and 100 Kg TNT at standoff distance of 10m and 30m from face of column at first floor level. The triangular impulse was applied as nodal time history at all front face joints. The analysis was performed using Computer aided software. The response of structure of will be evaluated under various blast scenarios. The response will be checked for safety of the structure on many parameters like displacement, acceleration and velocity.
Behavior of RCC Structural Members for Blast Analysis: A Review IJERA Editor
In today’s scenario threat of enemies and terrorist attack is increasing. Therefore consideration of blast load in analysis and design is essential. A bomb explosion within or nearby outside the building can cause catastrophic failure of building. Blast loads have, in the recent past, become important service loads for certain categories of structure. An important task in blast resistance design is to make a realistic prediction of blast pressure. The distance of explosion from the structure is an important datum, governing the magnitude and duration of blast loads. In the present study, the RCC frame was analyzed by using conventional code for gravity loads using moment resisting frame. The blast load was calculated using UFC-340-02 (2008) or IS 4991-1968 for 500 kg and 100 Kg TNT at standoff distance of 10m and 30m from face of column at first floor level. The triangular impulse was applied as nodal time history at all front face joints. The analysis was performed using Computer aided software. The response of structure of will be evaluated under various blast scenarios. The response will be checked for safety of the structure on many parameters like displacement, acceleration and velocity.
Structures to Resist the Effects of the Accidental Explosionsijtsrd
Currently in the field of civil engineering the requirement regarding knowledge blast loads are essential. Every country in the world are having terrorist threats. As the scenario of terrorist attacks are unpredictable neither location nor blast material used. This provides an outline to analysis and design to resist blast loads. We have taken an example model to illustrate evaluation of blast parameters which are used in the analysis. The analysis and design of structures to resist blast explosive loads is having utmost importance compared to the conventional type of structures. Where Loading is actually independent of time variation. From past few decades terrorist attacks are becoming a new threat to people lives material used, its quantity, and distance from structure etc. Since we dont know when the blasting activity is going to be happened and type of charge material is used, depends on importance of structure we have to make sure the design of structure should be such that it should resist the failure against blasting activities and to property also. The amount of damage caused to structure is depends upon type of charge. Blast loads, its contribution to structures and other required provisions are opted from Technical Manual 5 1300 and IS 4991 1968.The design method used is Equivalent Static Approach. Analysis of frames of structure is done with software package. Kota Sudeep | V. Narasimha Rao ""Structures to Resist the Effects of the Accidental Explosions"" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-3 , April 2019, URL: https://www.ijtsrd.com/papers/ijtsrd23455.pdf
Paper URL: https://www.ijtsrd.com/engineering/civil-engineering/23455/structures-to-resist-the-effects-of-the-accidental-explosions/kota-sudeep
Comparative Study of Response of Structures Subjected To Blast and Earthquake...IJERA Editor
The increase in the number of terrorist attacks especially in the last few years has shown that the effect of blast
load on building is a serious challenge that should be taken in to consideration for designing of structures. This
type of loading damages the structures, externally as well as internally. Hence the blast load should be
considered with same importance as earthquake load. The present study includes the comparative performance
of G+3 storey building subjected to blast and earthquake loading using ETABS. For four storey building using
different input parameters like charge explosive, stand-off distance and layout of building the blast pressure are
conducted and linear time history analysis is carried out. Comparative study for blast and earthquake loading is
carried out for different parameters like maximum storey displacement, storey drift and quantity of materials.
Safe charge explosive and safe stand-off distance are obtained for the RCC structure with the sections of
structural elements same as per the requirement for earthquake resistance. Displacement is higher for the blast
loading as compared to earthquake loading and very high for the storey at which blast load is applied. Quantity
of concrete is 40 percentages higher for blast resistant building than the earthquake resistant building.
EFFECT OF SEISMIC LOAD ON REINFORCED CONCRETE MULTISTORY BUILDING FROM ECONOM...IAEME Publication
This paper aims at studying the effect of earthquake loading on the constructional
design of a 20-storey reinforced concrete residential building from economical point
of view. This type of loading should be taken into considerations now in Iraq
especially after the earthquake of 7.3 magnitude that occurred in November 2017 near
the city of Halabja by about 31 kilometers. The same reinforced concrete multistory
building was designed twice; once with traditional gravity dead and live loading and
the second with adding earthquake loading in order to discuss the difference from
structural and economical points of view. A commercial package ETABS2018 was
used to analyze this 60-meter-high building. The building was analyzed according to
the American code ASCE7-10, while it was designed according to ACI 318-14. A huge
increase in the steel reinforcement amounts in columns, beams, slabs and shear walls
were recorded due to taking the seismic load into considerations. More specifically,
the reinforcing steel amounts increased by about 327%, 165%, 40% and 91.3% for
columns, beams, slabs and shear walls, respectively. Therefore, cost was raised by
about 328%, 165%, 40% and 91.3% for columns, beams, slabs and shear walls,
respectively. It is worth to mention here that the maximum increase in main
reinforcement of beams was observed on the storey 10. Whereas, in slabs, the
maximum increase that was recorded in main steel reinforcement was happened from
the storey 8 to the building top. In columns, the main reinforcement increase was seen
on the 9th, 10th and 11th storeys. Finally, in shear walls, the main reinforcement
increase was seen in the 1
st
, 2
nd
and 3
rd
storey due to effect lateral shear forces
Structural robustness analysis of RC frames under seismic and blast chained l...Franco Bontempi
In this paper the structural robustness assessment of concrete frame buildings under blast and under earthquake blast hazard chain scenarios is investigated. A deterministic methodology for connecting
the robustness with the blast hazard intensity and for conducting the robustness analysis under earthquake-triggered blast is presented and applied to a 3D RC frame building by implementing nonlinear time history analyses considering both plastic behavior and large displacements.
A preliminary sensitivity analysis on a 2D frame is conducted to identify the critical analysis
parameters influencing the results. The robustness curves (residual structural capacity versus the level of damage occurring in the structure), evaluated both for the blast-only and for the earthquake-blast chained cases, are compared by considering different explosion locations inside the building (location of the blast-induced structural damage). Results show that neglecting the chained load scenarios would lead to the identification of an erroneous location as critical for the
structural robustness performance.
Progressive collapse analysis in rc structure due to 150513181706pradip patel
Now in the recent time of terrorism, structural engineers require new consideration of terrorist attack in the design standards. Modern day structures pose a unique challenge to designers due to increased terrorist activities. Bomb blasts, vehicular attacks, Arson, Armed based attack all may result into a partial or total collapse of buildings. The work undertaken is an attempt to recognize the behaviour of RC structure under series blast loading. A model of G+4 RC structures has been considered as a progressive collapse analysis. The RC building with effect of series blast loading is analysed by using linear static and dynamic analysis. The present study work will carry out the effective study of different parameters like; different types of explosive charges (5T-5T, 7.5T-7.5T, 10T-10T TNT) at 10 mt. stand-off distance, failure of structure element at storey level and the structure is checked for progressive collapse by using commonly available, widely used software SAP 2000 will utilize for analysis
IRJET-Effect of Blast Loading on Framed Structure: A Review
Blast Loading
1. EFFECT OF BLAST LOADING ON RC STRUCTURES
A SEMINAR REPORT SUBMITTED IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF
Master of Engineering
in
Civil Engineering
By
ALOK B. RATHOD
Bhartiya Vidya Bhavan’s
SARDAR PATEL COLLEGE OF ENGINEERING, MUMBAI
DEPARTMENT OF CIVIL ENGINEERING
2014
2. Bhartiya Vidya Bhavan’s
SARDAR PATEL COLLEGE OF ENGINEERING, MUMBAI
DEPARTMENT OF CIVIL ENGINEERING
CERTIFICATE
This is to certify that Mr. ALOK BHAKTIRAM RATHOD Roll no. MCSI016 has
successfully completed the seminar work entitled “EFFECT OF BLAST LOADING ON
RC STRUCTURES” in the partial fulfillment of M.E. (Structural Engineering)
Date :
Place : Mumbai
3. ACKNOWLEDGEMENT
I wish to express my thanks to Prof. Dr. M.M. Murudi, Head of the Civil
Engineering Department, and Prof. Dr. A. A. Bage for being there throughout the
completion of this Report.
I also express my deep sense of gratitude to all my Professors, Department of
Structural Engineering, Sardar Patel College of Engineering, Mumbai for valuable
guidance, constant encouragement and creative suggestions offered during the course
of this seminar and also in preparing this report.
Date: Alok B. Rathod
Place: Mumbai Roll No. MCSI-016
SPCE, Mumbai
4. I
CONTENTS
CHAPTER NO. TITLE PAGE NO.
ABSTRACT
lll
LIST OF FIGURES
lV
LIST OF TABLES
V
CHAPTER 1 INTRODUCTION 1
1.1 Critical Review 1
1.2 Introduction 1
CHAPTER 2 REVIEW OF LITERATURE 2
2.1 General 2
2.2 Objective and scope of the present work 5
2.2.1 Objective 5
2.2.2 Scope of the study 5
CHAPTER 3 BACKGROUND 6
3.1 Explosion and blast phenomenon 6
3.1.1 Shock waves or blast waves 6
3.1.2 Dynamic loadings 8
3.2 Effects on structures 8
3.3 Structural response or analysis to blast loadings 10
5. II
CHAPTER 4 CASE STUDIES 12
4.1 Column subjected to blast loadings 12
4.2 Reinforced concrete panels subjected to blast loadings 13
4.2.1 Test specimens 13
4.2.2 Test setting 15
4.2.3 Measurement outline 15
4.2.4 Test results 16
CHAPTER 5 CONCLUSION AND FUTURE SCOPE 20
5.1 Conclusions 20
5.2 Future scope of study 20
REFERENCES 21
6. III
ABSTRACT
A bomb explosion within or immediately nearby a building can cause catastrophic damage on the
building's external and internal structural frames, collapsing of walls, blowing out of large
expanses of windows, and shutting down of critical life-safety systems. Loss of life and injuries to
occupants can result from many causes, including direct blast-effects, structural collapse, debris
impact, fire, and smoke. The indirect effects can combine to inhibit or prevent timely evacuation,
thereby contributing to additional casualties.
In addition, major catastrophes resulting from gas-chemical explosions result in large dynamic
loads, greater than the original design loads, of many structures. Due to the threat from such
extreme loading conditions, efforts have been made during the past three decades to develop
methods of structural analysis and design to resist blast loads. Studies were conducted on the
behavior of structural concrete subjected to blast loads. These studies gradually enhanced the
understanding of the role that structural details play in affecting the behavior.
The response of simple RC columns subjected to constant axial loads and lateral blast loads was
examined. Also slab panel subjected to various blast loadings was examined, which were made
out of different mix and polymers. Next, a short duration, lateral blast load was applied and the
response time history was calculated.
The analysis and design of structures subjected to blast loads require a detailed understanding of
blast phenomena and the dynamic response of various structural elements. This gives a
comprehensive overview of the effects of explosion on structures.
7. IV
LIST OF FIGURES
FIGURE NO. TITLE PAGE NO.
Fig no. 3.1 Blast wave propagation 6
Fig no. 3.2 Generalized Blast Pressure History 7
Fig no. 3.3 Blast loads on buildings 8
Fig no. 3.4 Blast Pressure Effects on a Structure 9
Fig no. 3.5 3.5 (a) SDOF System 10
3.5 (b) Blast Loading 10
Fig no. 4.1 Simplified Blast Loading 12
Fig no. 4.2 3D model of the column using explicit code LS-Dina 13
Fig no. 4.3 Test specimen geometry 14
Fig no. 4.4 Overview of supporting steel box 15
Fig no. 4.5 Test Setup 15
Fig no. 4.6 Sensor location of the concrete specimen 16
4.6 (a) Steel Strain 16
4.6 (b) Concrete Strain 16
Fig no. 4.7 Blast pressure on concrete specimen 16
4.7 (a) Free field pressure on CFRP 16
4.7 (b) Reflect pressure on CFRP 16
Fig no. 4.8 Behavior of conc. specimen (NSC, CFRP) 18
Fig no. 4.9 Error bar of disp. under blast loading 18
Fig no. 4.10 Error bar of disp. under blast loading 18
4.10(a) Normal strength concrete specimen 18
4.10(b) Failure of each FRP specimen 18
8. V
LIST OF TABLES
TABLE NO. TITLE PAGE NO.
Table No. 4.1 Mixed proportion of concrete slab specimen 14
Table No. 4.2 Material properties of retrofitted materials 14
Table No.4. 3 Blast test results 17
9. 1
CHAPTER 1
INTRODUCTION
1.1 CRITICAL REVIEW
The blast explosion nearby or within structure is due to pressure or vehicle bomb or quarry
blasting. These causes catastrophic damage to the building both externally and internally
(structural frames). Resulting in collapsing of walls, blowing out of windows, and shutting down
of critical life-safety systems. Buildings, bridges, pipelines, industrial plants dams etc. are the
lifeline structures and they play an important role in the economy of the country and hence they
have to be protected from dynamic and wind loading.
These structures should be protected from the blast effects, which are likely to be the targets of
terrorist attacks. The dynamic response of the structure to blast loading is complex to analyze,
because of the non- linear behavior of the material. Explosions result in large dynamic loads,
greater than the original design loads, for which the structures are analyzed and designed.
Analyses and design of blast loading requires detailed knowledge of blast and its phenomena. A
critical review is presented in this paper to estimate the blast loading and its dynamic effects on
various components of structure treating the effects as SDOF system.
1.2 INTRODUCTION
The study of blast effects on structures has been an area of formal technical investigation for
over 60 years. A bomb explosion within or immediately nearby a building can cause catastrophic
damage on the building's external and internal structural frames, collapsing of walls, blowing out
of large expanses of windows, and shutting down of critical life-safety systems. Loss of life and
injuries to occupants can result from any causes,including direct blast-effects,structural collapse,
debris impact, fire, and smoke. The indirect effects can combine to inhibit or prevent timely
evacuation, thereby contributing to additional casualties. In addition, major catastrophes
resulting from gas-chemical explosions result in large dynamic loads, greater than the original
design loads, of many structures.
Strategies for blast protection have become an important consideration for structural designers
as global terrorist attacks continue at an alarming rate. Conventional structures normally are not
designed to resist blast loads and because the magnitudes of design loads are significantly lower
than those produced by most explosions, conventional structures are susceptible to damage
from explosions. No civilian buildings can be designed to withstand the kind of extreme attack
that happened to the World Trade Centre in USA. Building owners and design professionals alike,
however, can take steps to better understand the potential threats and protect the occupants
and assets in an uncertain environment. With this in mind, developers, architects and engineers
increasingly are seeking solutions for potential blast situations, to protect building occupants and
the structures.
10. 2
CHAPTER 2
REVIEW OF LITERATURE
2.1 GENERAL
In the past, few decades’ considerable emphasis has been given to problems of blast and
earthquake. The earthquake problem is rather old, but most of the knowledge on this subject has
been accumulated during the past fifty years. The blast problem is rather new; information about
the development in this field is made available mostly through publication of the Army Corps of
Engineers, Department of Defense, U.S. Air Force and other governmental office and public
institutes.
Much of the work is done by the Massachusetts Institute of Technology, The University of Illinois,
and leading educational institutions and engineering firms. Due to different accidental or
intentional events, the behavior of structural components subjected to blast loading has
been the subject of considerable research effort in recent years. Conventional structures are
not designed to resist blast loads; and because the magnitudes of design loads are
significantly lower than those produced by most explosions. Further, often conventional
structures are susceptible to damage from explosions. With this in mind, developers, architects
and engineers increasingly are seeking solutions for potential blast situations, to protect building
occupants and the structures.
This study is very much useful for design the buildings constructed for industries where chemical
process is the main activity. An increasing number of research programs on the sources of these
impact loads a dynamic analysis and preventive measures are being undertaken. Just in design
some areas takes into account the effects of earthquakes, hurricanes, tornadoes and
extremes snow loads, likewise even explosive or blast loads has to be taken into design
consideration. This does not mean design and consideration of specialshelter facilities but simply
the application of appropriate design techniques to ordinary buildings, so that one can achieve
some degree of safety from sudden attacks.
Philip Esper in 2003, after the Four major bombing incidents took place in Mainland UK within
the last ten years; the 1992 St Mary's Axe, the 1993 Bishopsgate, the 1996 Docklands and
Manchester bombs the author was involved in the investigation of damage and reinstatement of
numerous commercial buildings, and in providing advice to building owners and occupiers on
blast protection measures for both existing and proposed buildings. These detonation devices
were estimated as 450 kg, 850 kg, 500 kg and 750 kg of TNT equivalent, respectively. As a result,
the author was involved in the investigation of damage and reinstatement of numerous
commercial buildings, and in providing advice to building owners and occupiers on blast
protection measures for both existing and proposed buildings. Numerical modeling as well as
laboratory and on-site testing were used in the investigation of damage and assessing the
dynamic response of these buildings and their floor slabs to blast loading. The finite element (FE)
11. 3
analysis technique used in this investigation is described, and the correlation between the results
of the FE analysis and laboratory and on-site testing is highlighted. It was concluded that the
ductility and natural period of vibration of a structure governs its response to an explosion.
Ductile elements, such as steel and reinforced concrete, can absorb significant amount of strain
energy, whereas brittle elements, such as timber, masonry, and monolithic glass, fail abruptly.
LUCCIONI et al in 2005, studied the effects of mesh size on pressure and impulse distribution of
blast loads with the aid of hydro-codes. A computational dynamic analysis using AUTODYN-3D
was carried out over the congested urban environment that corresponds to the opposite rows of
buildings of a block, in the results obtained for different positions of the explosive charge are
presented and compared. The effect of mesh size for different boundary conditions is also
addressed. It is concluded that the accuracy of numerical results is strongly dependent on the
mesh size used for the analysis. On the other side the mesh size is also limited by the dimensions
of the model and the computer capacity. One of the major features in the numerical simulation
of blast wave propagation in large urban environments is the use of an adequate mesh size.
The accuracy of numerical results is strongly dependent on the mesh size used for the analysis. A
10 cm mesh is accurate enough for the analysis of wave propagation in urban ambient.
Nevertheless, it may be too expensive to model a complete block with this mesh size.
Alternatively, a coarser mesh can be used in order to obtain qualitative results for the comparison
of the loads produced by different hypothetical blast events. Even coarse meshes, up to 50 cm of
side, give a good estimation of the effects of moving the location of the explosive charges.
Ghani Razaqpur et al in 2006, investigated the behavior of reinforced concrete panels, or slabs,
retrofitted with glass fiber reinforced polymer (GFRP) composite, and subjected to blast load
Eight 1000 x 1000 x 70 mm panels were made of 40 MPa concrete and reinforced with top and
bottom steel meshes. Five of the panels were used as control while the remaining four were
retrofitted with adhesively bonded 500 mm wide GFRP laminate strips on both faces, one in each
direction parallel to the panel edges. The panels were subjected to blast loads generated by the
detonation of either 22.4 kg or 33.4 kg ANFO explosive charge located at a 3-m standoff. Blast
wave characteristics, including incident and reflected pressures and impulses, as well as panel
central deflection and strain in steel and on concrete/FRP surfaces were measured. The post-
blast damage and mode of failure of each panel was observed, and those panels that were not
completely damaged by the blast were subsequently statically tested to find their residual
strength. It was determined that the reflected blast pressure and impulse measured at the same
location during different shots using the same charge size and standoff distance were generally
reasonably close, but in some cases significant deviation occurred. The results of this study
indicate that the GFRP retrofit may not be suitable in every situation and that quantifying its
strengthening effects will need more actual blast testing rather than merely theoretical modeling
or pseudo-dynamic testing.
12. 4
Ray Singh Meena in 2009, focused on the design techniques for the loading on roof structures
and the resistance of open web steel joists, a common roof component. Blast loads are dynamic,
impulsive and non-simultaneous over the length of a roof.
To design against explosions, a procedure has been developed to devise a uniform dynamic load
on a roof that matches the response from blast loads. The objective of this research was to test
and compare its results to the deflections from blast loads using FEM of analysis and to compare
them to equivalent loading response. It is recommended that additional research is to be done
on the prediction of blast pressures on roofs and on the development of an equivalent uniform
dynamic load. It is also recommended that an analytical resistance function for open web steel
joists be clearly defined, which includes all failure limit states.
Ngo ET AL in 2007, carried an analytical study on RC column subjected to blast loading and
progressive collapse analysis of a multi-storied building were carried out. The 3D model of the
column was analyzed using the nonlinear explicit code LS-Dyna 3D (2002) which takes into
account both material nonlinearity and geometric nonlinearity. It was observed that the increase
in flexural strength was greater than that of shear strength. Thus, the increase in the material
strengths under dynamic conditions may lead to a shift from a ductile flexural failure to a brittle
shear failure mode. In the progressive collapse analysis study which is based on the local
damage assessment due to bomb blast at ground level, progressive collapse analyses was
performed on the example building. The structural stability and integrity of the building were
assessed by considering the effects of the failure of some perimeter columns, spandrel beams
and floor slabs due to blast overpressure or aircraft impact. In addition to material and geometric
nonlinearities, the analyses considered membrane action, inertia effects, and other influencing
factors. The results show that the ultimate capacity of the floor slab is approximately 16.5kPa
which is 2.75 times the total floor load (dead load plus 0.4 live load).
Alok Goyal in 2008, discussed through an overview to quantify blast loads as high pressure, short
duration shock loading for the building as a whole and on each individual structural component.
The study concluded that the most difficult part of the blast-resistance design is to define the
blast wave parameters with acceptable probability of exceedance, and to quantify desired
performance parameters in terms of crack widths, rotations, ductility factor capacities of
elements or story drifts. Considerable efforts and skill is required to numerically predict the blast
induced pressure field and highly non-linear response. Even then, the results may be meaningless
due to modeling limitations and uncertainties associated with blast loads. The developed systems
therefore should be tested in field and the data collected should be used to improve the design
and the mathematical model.
13. 5
2.2 OBJECTIVE AND SCOPE OF THE PRESENT WORK
2.2.1 OBJECTIVE:
To analyze and design the structures against the abnormal loading conditions like blast loads,
strong wind pressure etc. requiring detailed understanding of blast phenomenon.
To study the dynamic response of various structural elements like column, beam, slab and
connections in steel and RCC structures.
The main objective of the research presented in this report is to analytically and
numerically study the structural behavior of HSC and NSC column subjected to blast loading.
2.2.2 SCOPE OF THE STUDY:
In order to achieve the above-mentioned objectives the following tasks have been carried out:
All the computation of dynamic loading on a rectangular structure with and without openings
and open frame structures to evaluate the blast pressure.
Computation of the blast loading on the column.
Modeling of a simple RC column in ANSYS.
Response of a simple RC column under the Blast loading.
14. 6
CHAPTER 3
BACKGROUND
3.1 EXPLOSION AND BLAST PHENOMENON
An explosion is a rapid release of stored energy characterized by a bright flash and an audible
blast. Part of the energy is released as thermal radiation (flash); and part is coupled into the air
as air-blast and into the soil (ground) as ground shock, both as radially expanding shock waves.
To be an explosive, the material will have the following characteristics.
1. Must contain a substance or mixture of substances that remains unchanged under ordinary
conditions, but undergoes a fast chemical change upon stimulation.
2. This reaction must yield gases whose volume—under normal pressure, but at the high
temperature resulting from an explosion—is much greater than that of the original
substance.
3. The change must be exothermic in order to heat the products of the reaction and thus to
increase their pressure. Common types of explosions include construction blasting to break
up rock or to demolish buildings and their foundations, and accidental explosions resulting
from natural gas leaks or other chemical/explosive materials.
3.1.1 SHOCK WAVES OR BLAST WAVES
The rapid expansion of hot gases resulting from the detonation of an explosive charge gives rise
to a compression wave called a shock wave (Fig1), which propagates through the air. The front
of the shock wave can be considered infinitely steep, for all practical purposes. That is, the time
required for compression of the undisturbed air just ahead of the wave to full pressure just
behind the wave is essentially zero. From the figure 1 it can be concluded that if the explosive
source is spherical, the resulting shock wave will be spherical, since its surface is continually
increasing, the energy per unit area continually decreases.
Fig 3.1: Blast wave propagation
15. 7
Consequently, as the shock wave travels outward from the charge, the pressure in the front of
the wave, called the peak pressure, steadily decreases. At great distances from the charge, the
peak pressure is infinitesimal, and the wave can be treated as a sound wave. Behind the shock
wave front, the pressure in the wave decreases from its initial peak value. At some distance from
the charge, the pressure behind the shock front falls to a value below that of the atmosphere and
then rises again to a steady value equal to that of the atmosphere. The part of the shock wave in
which the pressure is greater than that of the atmosphere is called the positive phase and,
immediately following it, the part in which the pressure is less than that of the atmosphere is
called the negative or suction phase.
The rapid oxidation of fuel elements develops chemical explosions. This reaction releases
heat and produces gas, which expands. Low-end explosives create quasi static loads. High
explosives (chemical and nuclear) in a surrounding medium, such as air or water, cause shock
waves in the medium. The blast releases high-pressure gases at high tempera- tires. These gases
naturally expand, and the surrounding medium is consequently compressed. The compressed
medium, or for the specific case of air, forms a shock front. The shock front travels in a radial
direction. As the explosive gases cool and slow their movement, the amount of "overpressure"
the shock front carries decreases. The gases release energy to reach equilibrium towards the
atmospheric pressure.
Fig 3.2: Generalized Blast Pressure History
However, due to the high pressure and mass of the gases, more expansion is necessary to actually
reach equilibrium. This causes the pressure in the shock wave to drop below the atmospheric
pressure. After sufficient "under pressure" is expended, the state returns to the atmospheric
pressure. The air behind the shock front also places a load, a drag force, on objects encountered.
The general shape of a pulse shape is shown in Figure 2. Important factors pertinent to burst
pressures include the peak pressure, the duration, the air density behind the shock front, the
velocity of the shock front, and the impulse of the blast pressure.
16. 8
3.1.2 DYNAMIC LOADINGS
Drag exerted by the blast winds required to form the blast wave. These winds push, tumble and
tear objects. Blast pressure can create loads on buildings that are many times greater than
normal design loads (Fig 3), and blast winds can be much more severe than hurricanes. Buildings
with relatively weak curtain walls and interior partitions would probably be gutted very early
during the blast phase, even at low over pressures. Dynamic pressures would then continue to
cause drag loads on the structural frames that is left standing. Slabs over closed basements
would experience the downward thrust of over-pressure, which would be transmitted to
supporting beams girders and columns. Foundation would experience blast induced vertical and
overturning forces.
Fig 3.3: Blast loads on buildings
Failure would occur unless the structural system was designed to resist these large quickly
applied loads. Structures with load bearing walls or curtain walls that not blowout easily could
be completely demolished or toppled by blast loads. Such structures would experience the
combined loading conditions caused by the incident overpressure, the dynamic and highly
transient reflected pressure that develop when the shock waves strikes a surface of the
structure. People in the basement shelters who are protected against catastrophic structural
collapse, high pressure and flying objects would have the greatest possibility of surviving the blast
phase.
3.2 EFFECTS ON STRUCTURES
Blast effects on building structures can be classified as primary effects and secondary effects.
Primary effects include;
1. Air-blast: The blast wave causes a pressure increase of the air surrounding a building structure
and also a blast wind.
17. 9
2. Direct ground shock: An explosive which is buried completely or partly below the ground
surface will cause a ground shock. This is a horizontal (and vertical, depending on the location of
the explosion with regard to the structural foundation) vibration of the ground, similar to an
earthquake but with a different frequency.
3. Heat: A part of the explosive energy is converted to heat. Building materials are weakened at
increased temperature. Heat can cause fire if the temperature is high enough.
4. Primary fragments: Fragments from the explosive source which are thrown into the air at high
velocity (for example wall fragments of an exploded gas tank). Secondary effects can be
fragments hitting people or buildings near the explosion. They are not a direct threat to the
bearing structure of the building, which is usually covered by a facade. However, they may
destroy windows and glass facades and cause victims among inhabitants and passers-by.
Blast loading on structures can be explained by three main loading conditions (figure4)
1. In the first type a relatively large shock wave reaches a structure relatively small enough
that the blast wave encloses the entire structure. The shock wave effectively acts on the
entire structure simultaneously. Additionally, there is a drag force from the rapidly moving
wind behind the blast wave. The structure is, however, massive enough to resist translation.
Fig 3.4: Blast Pressure Effects on a Structure
2. The second condition also involves a relatively large shock wave and a target much smaller
than the previous case. The same phenomena happen during this case, but the target is
sufficiently small enough to be moved by the dynamic, drag pressure.
18. 10
3. In the final case, the shock burst is too small to surround the structure simultaneously and
the structure is too large to be shifted. Instead of simultaneous loading, each component
is affected in succession. For a typical building, the front face is loaded with a reflected
overpressure.
3.3 STRUCTURAL RESPONSE OR ANALYSIS TO BLAST LOADING
Blast loading is a short duration load also called impulsive loading. Mathematically blast loading
is treated as triangular loading. The ductility and natural period of vibration of a structure governs
its response to an explosion.
Ductile elements, such as steel and reinforced concrete, can absorb significant amount of strain
energy, whereas brittle elements, such as timber, masonry, and monolithic glass, fail abruptly. In
the investigation of the dynamic response of a building structure to bomb blast, the following
procedures are followed
(a) The characteristics of the blast wave must be determined; (b) the natural period of response
of the structure (or the structural element) must be determined; (c) The positive phase duration
of the blast wave is then compared with the natural period of response of the structure. Based
on (c) above, the response of the structure can be defined as follows:
i. If the positive phase duration of the blast pressure is shorter than the natural period of
vibration of the structure, the response is described as impulsive. In this case, most of the
deformation of the structure will occur after the blast loading has diminished.
Fig 3.5: (a) SDOF system (b) Blast loading
ii. If the positive phase duration of the blast pressure is longer than the natural period of
vibration of the structure, the response is defined as quasi-static. In this case, the blast will
cause the structure to deform whilst the loading is still being applied.
iii. If the positive phase duration of the blast pressure is close to the natural period of vibration
of the structure, then the response of the structure is referred to as dynamic. In this case, the
19. 11
deformation of the structure is a function of time and the response is determined by solving
the equation of motion of the structural system.
Equation of motion for an undamped forced system is given by
MŸ (t) + KÝ (t) = F (t) - - - - - - - - - - (a)
The force is given by
F (t) = F0 (1- T / td) - - - - - - - - - - (b)
Initial conditions for triangular pulse is Y0=0, V0= 0
The total displacement of an un-damped SDOF system is given by
Y (t) = Y0 cosωt + (V0 /ω) sinωt + 1/mω∫t0
F (t) sinω (t-T) dt- - - - - - (c)
Displacement
Y (t) = Fm/K (1-cosωt) + Fm/ktd ((sinωt/ω) –t) - - - - - - - - - - - - - - (d)
Velocity
Ý (t) =dy/dt= Fm/K [ωsinωt+1/td (cosωt-1)] - - - - - - - - - - - - - - - - (e)
In which ω is the natural circular frequency of vibration of the structure and T is the natural period
of vibration of the structure which is given by equation
ω = 2π/T √=K/M - - - - - - - - - - - - (f)
The maximum response is defined by the maximum dynamic deflection Ym which occurs at time
tm. The maximum dynamic deflection Ym can be evaluated by setting dy/dt in Equation (c) equal
to zero, i.e. when the structural velocity is zero. The dynamic load factor, DLF, is defined as the
ratio of the maximum dynamic deflection Ym to the static deflection Yst which would have
resulted from the static application of the peak load Fm, which is shown as follows:
DLF=Ym / Yst - - - - - - - - - - - - - - (g)
DLF=1/ (2πtd/T) {sin2π (t/T) - sin2π (t/T - td/T)} - cos2π t/T - - - - - - (h)
The dynamic load factor of blast loading is given by equation (h) to be considered in evaluating
the correctness of evaluating the dynamic stresses.
20. 12
CHAPTER 4
CASE STUDIES
4.1 COLUMN SUBJECTED TO BLAST LOADING
A ground floor column of a multi-storey building was analyzed. The parameters considered were
the concrete strength (40MPa for NSC column and 80 MPa HSC column) and spacing of
ligatures (400mm for ordinary detailing-OMRF (ordinary moment resisting frame) and 100mm
for special seismic detailing-SMRF (seismic moment resisting frame)). It has been found that with
increasing concrete compressive strength, the column size can be effectively reduced. In this case
the column size was reduced from 500 x 900 mm for the NSC column down to 350 x 750 for the
HSC column.
Fig 4.1: Simplified blast loading
While the axial load capacities of the two columns are stillthe same. The blast load was calculated
based on data from the Oklahoma bombing report (ASCE 1996) with a standoff distance of 11.2m.
The simplified triangle shape of the blast load profile was used (fig 6). The duration of the positive
phase of the blast is 1.3 milliseconds. The 3D model of the column was analyzed using the
nonlinear explicit code LS-Dina 3D (fig 7) (2002) which takes into account both material
nonlinearity and geometric nonlinearity. The strain rate- dependent constitutive model proposed
in the previous section was adopted. The effects of the blast loading were modeled in the
dynamic analysis to obtain the deflection time history of the column.
From this case study on the response of HSC and NSC columns subjected to bomb blast a strain-
rate dependent constitutive model for concrete is proposed which is applicable to both normal
strength and high strength concretes. It was found that shear failure was the dominant modes of
failures for close-range explosion. HSC columns were shown to perform better than NCS columns
(with the same axial load capacity) when subjected to extreme impulsive loading, they also
had higher energy absorption capacity. Results from the study concluded that the impulsive
21. 13
loading is very different from the static loading in terms of the dynamic inertia effect and
structural response.
Fig 4.2: 3D model of the column using explicit code LS-Dina
4.2 REINFORCED CONCRETE PANELS
4.2.1 TEST SPECIMENS
As shown in Figure 2, nine 1000 × 1000 × 150 mm reinforced concrete slab specimens with double
lattice reinforcements with 12-D10 steel bars with 82mm regular spacing in each direction were
made for the experiment. The bar yield strength and ultimate strength are 400 MPa and 600
MPa, respectively. The average 28day concrete compressive strength is 24 MPa and the average
compressive strength at the age of testing is 25.6 MPa. The mix proportion of concrete slab
specimens is shown in Table 1. The specimens include NSC (normal strength concrete; the control
specimen), CFRP (carbon fiber reinforced polymer), polyurea (same thickness as CFRP specimen),
BFRP (basalt fiber reinforced polymer), and CFRP with polyurea specimen. CFRP and BFRP
specimens were retrofitted to concrete on one side with 2 layers. And polyurea are sprayed to
concrete with same thickness as CFRP.
Also, total retrofitted thickness of CFRP with polyurea specimens is same as the other retrofitted
specimens with sprayed on the specimen with one layer of CFRP sheet. Two specimens are made
for each case except for the BFRP specimen.
22. 14
Fig 4.3: Test specimen geometry
Table 4.1. Mixed proportion of concrete slab specimen
Table 4.2. Material properties of retrofitted materials
23. 15
4.2.2 TEST SETTING
As shown in Figure 3, the test specimen is placed on a buried steel frame box in the ground. This
setting system can eliminate the clearing effect by the ground surface acting as a target of infinite
dimensions with the test specimen being part of this unlimited surface (Razaqpur et al. 2007).
The specimen placed on the buried steel box is fixed by clamps used to prevent uplift and keep
the consistent boundary condition. Rubber pads of the same width and length as the steel angle
legs were placed between the angles and test specimen to ensure uniform support conditions.
The explosive used for the test was spherical ANFO, which was held by wood horizontal bar.
Figure 4 shows the test specimen setup with the 35lbs ANFO (28.7lbs TNT) explosive charge. The
1.5m standoff from specimens to explosive middle point is consistently maintained.
Fig 4.4: Overview of supporting steel box Fig 4.5: Test setup
4.2.3 MEASUREMENT OUTLINE
The free field incident pressure was measured at 5m from the center of the test slab specimens
as shown in Figure 3 where reflected pressure on concrete specimen was measure at the center
of the top surface of the specimen and 230mm from the center between the center and 1/3 point
of specimen diagonal length. To measure strain, 6mm strain gauges are attached on tensile part
of steel and 30mm strain gauges are attached on concrete upper and lower surfaces as shown
Figure 5. In case of retrofitted specimen,FRP strain gauges are attached instead of concrete strain
gauges on bottom surface. Also, LVDTs on the specimen center are used to measure the
maximum and residual displacements. The data acquisition systems used are Dewe 2010 and
Dewe 5000.
24. 16
(a) Steel strain (b) concrete strain
Fig 4.6: Sensor location of the concrete specimen
4.2.4 TEST RESULTS
The measured free field pressure for the test of CFRP specimen is similar with the analysis blast
pressure results obtained using ConWEP as shown in Figure 6(a). In case of reflected pressure on
concrete surface, specimen (Figure 6(b)) was applied with a secondary pressure due to sequential
detonation of ANFO charge. But, this type of sequential pressure load was observed in the
simulation using ConWEP. The duration of reflected pressure is less than 0.5msec, which shows
that the high pressure was applied to the specimen for a very short duration. The applied impulse
which is constituted by pressure and duration is shown in Table 1 and the reflected impulse is
generally 10 times greater than the free field pressure in this test.
(a) Free field pressure on CFRP (b) Reflect pressure on CFRP
Fig 4.7: Blast pressure on concrete specimen
25. 17
Although NSC 1 was charged with TNT 35 lbs. for preliminary test, the reflected pressure on
specimen did not recognize the signal. Therefore, based on the preliminary test, ANFO 35lbs was
selected as an appropriate charge.
In Table 1, the maximum strains of steel rebar and concrete/FRP obtained at the center of the
specimens are tabulated. The results showed that all of bottom steels have yielded where as
some have and have not yielded in top steels. The strain gauges for concrete and FRP attached
at the top and bottom surfaces showed large strains, which means the specimens have gone
through significant damages and plastic deformations, generally exceeding 10,000 με. Even
though the concrete strain has exceeded allowable strain, the residual strain was nearly 1,000
~5,000 με, showing great recovery. From the test results, it can be concluded that the retrofitted
FRP concrete specimen has a great ability to recover strain and a sufficient ductility.
Table 4.3: Blast test results
The maximum and residual displacements of each specimen were measured at the center of the
specimen. To measure specimen behavior under blast loading as shown in Figure 3, LVDT is
connected to the specimen. From this time-displacement relationship, frequency of the
specimens under blast load is measured and compared to the analytical results. As shown in
Figure 4, the results vary significantly from a specimen to a specimen due to variabilities in
environmental conditions and explosive charge shape. Therefore, the average displacements are
compared. In case of maximum displacement, CFRP with polyurea (CPU) specimen shows
smallest displacement due to combination highly ductile material of polyurea and highly stiff and
strong material of CFRP. Polyurea specimen does not have sufficient stiffness compared to CFRP
specimen. The maximum displacement of BFRP specimen is similar to CFRP specimen, but its
residual displacement is nearly large as the NSC specimen. It seems that the BFRP is an
26. 18
inappropriate blast strengthening material if residual displacement is an important parameter.
In case of maximum displacement, CFRP, polyurea, CPU and BFRP have retrofitted effect of
21.4%, 15.7%, 37.4% and 19.8%, respectively. And for residual displacement,CFRP,polyurea,CPU
and BFRP with respect to NSC have retrofitted effects of 67.4%, 43.0%, 63.7% and -11.3%,
respectively.
Fig 4.8: Behavior of conc. specimen (NSC, CFRP) Fig 4.9: Error bar of disp. under blast loading
Even though the displacement is one of the estimating parameter for retrofit effect, significant
variations and uncertainties can exist. To assess the effectiveness of each strengthening method,
the specimens were inspected for cracking, spalling, and delamination. The crack pattern of NSC
specimen of bottom surface is shown in Figure 5(a). The damages are concentrated at the center
and the overall crack pattern follow concrete yield line. Also, the NSC specimens show a shear
failure compared to retrofitted specimens, which show a bending failure. The retrofitted
specimens show de-bonding failure in interface of FRP and concrete surface. Also, local concrete
crushing has been observed around supported edges in FRP strengthened specimen due to more
rigidity.
(a) Normal strength concrete specimen (b) Failure of each FRP specimen
Fig 4.10: Failure mode each specimen under blast loading
27. 19
However, the retrofitted specimens generally suffered less damage than the control specimens
from the perspective of cracking and overall concrete failure. It can be safely concluded that
retrofitted FRP can sufficiently absorb the energy due to blast load.
28. 20
CHAPTER 5
CONCLUSION AND FUTURE SCOPE
5.1 CONCLUSIONS
From this study, various externally bonded strengthened RC slabs’ response induced by explosive
blast wave pressure are evaluated to understand the retrofit effect. The reflected blast pressure
and impulse values calculated using the ConWEP were in reasonable agreement with the
experimental data. The performance of retrofitted specimens compared to control specimens
when subjected to blast loads of ANFO 35 lbs. has shown the retrofitted effect about 15~38% for
maximum displacement. An average of retrofitted residual displacements was higher than
normal strength concrete specimen’s residual displacement, even though there was no
consistent trend due to various environmental conditions. Therefore, to evaluate the damage
under blast load, failure mode must be considered. From the test results, the retrofitted FRP
specimen has shown bending failure proving that retrofitted FRPs can be used for structural blast
strengthening.
5.2 FUTURE SCOPE OF STUDY
1. Cases in which the axial load does not remain constant during the column response time are
possible. These include situations where the bomb is located within the structure and the
blast excites the girders connected to the column. The effect of this time-varying axial load
should be studied.
2. Cases should be studied when the explosions within a structure can cause failure of interior
girders, beams and floor slabs.
3. Tests and evaluation of connections under direct blast loads.
4. Tests and design recommendations for base plate configurations and designs to resist direct
shear failure at column bases.
29. 21
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