Ijciet 10 01_167-2-3

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 01, January 2019, pp. 1801-1816, Article ID: IJCIET_10_01_167
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=01
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
OPTIMUM PRESTRESSING AMOUNT AND ITS
EFFECTIVE FORCE ON PRESTRESSED
CONCRETE DOUBLE TEE BEAM WITH WEB
OPENING
Hussam Ali Mohammed
Consultant of Structural Engineering, Al-Furat Al-Awsat Technical University /Al-Mussaib
Technical Collage
ABSTRACT
Double tees shows it's an excellent choice for parking decks and used in roof
applications where a long, clear span is required such as gyms and pools. Spans up to
22m can be achieved using Precast Double Tees. Double Tees are pre-fabricated
members on plants, which provides excellent quality control and speeds up the
construction process. Double tee slabs can be used for most applications requiring a
long span floor or roof system (10 m to +30 m) and/or additional load carrying
capability. More than that, Double tee slabs prove it has a good resistant to moisture
and corrosion. Parking garages, commercial buildings , office buildings, pool roofs
,gymnasiums, food processing plants, industrial buildings, paper mills, and water and
sewage treatment plants are all ideal applications. One or both ends of the slabs can
be cantilevered at for up to four times the slab depth. Double tee slabs are prestressed.
Which will increase the ability to carry heavy loads with allows for longer spans,
shallow depth. Further its permits better space planning and a lower floor/floor height.
Lengthening the span may be economical (fewer s labs to make and install). Maximum
span/depth ratios of forty almost be recommended for floors. Double-tees regularly be
used for many types of buildings structures. They are easily shipped and erected, very
economical, readily available, and contribute to early building occupancy.
Within three phase of study, started by prediction a powerful tool to simulate the
full behavior of prestressed concrete double tee beams with web openings under
flexure, and continue on its second phase by considering the effect of increasing
concrete compressive strength on the obtaining long span length, to this research study
(3rd phase) where the an optimization process carried out to check the effect of varying
the prestressing tendon value and its effective applied force. The effect of increasing
the prestressing force was clearly shown at plastic regain its start effect the
performance. Improving behaviour with higher moment capacity is the general view of
all tested samples reached 50%-78% comparing to the control beam without web
opening. While for varying the value of prestressing tendons, the beams with web

Optimum Prestressing Amount and Its Effective Force on Prestressed Concrete Double Tee Beam
with Web Opening
opening shows a reduction on its ultimate moments by 61%, 65%, and 61.5% for
reducing two tendons, while its show improvement reach 16%, 33%, and 34% when
increasing two tendons. Curves are classified and presented considering the most
common typical sections of the double tee beams modified to show the flexibility could
be obtained when changing concrete compressive strength.
Keyword head: Keyword text, Keyword text, Keyword text and Keyword text.
Cite this Article: Hussam Ali Mohammed, Optimum Prestressing Amount and Its
Effective Force on Prestressed Concrete Double Tee Beam with Web Opening,
International Journal of Civil Engineering and Technology, 10(01), 2019, pp. 1801–
1816
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=01
1. INTRODUCTION
Double tees in common used primarily as floor and roof components for any type of structure,
including parking structures, office buildings and industrial buildings. They are made either
pre-topped or field topped. Pre-topped tees have a flange thickness of 10cm, which creates the
wearing surface in parking structures. Field-topped tees have a 5cm flange, on which a cast-in-
place concrete composite topping of 5-10cm is added in the field. For roof construction, there
is typically no need to add topping on the 5cm flange. Tees typically are made in four widths
(2.4, 3, 3.6 and 4.6 m) and six depths (600, 660, 710, 760, 810 and 860 mm). Usually span-to-
depth ratios for floors range between 25 – 35m, while roofs typically are 35 - 40. Double tees
typically are cast in 90- to 150m-long prestressing facilities that are sub-divided into specific
lengths for a particular project.
This natural flexibility makes double tees the best option for building structures that feature
long spans and that do not require additional ceiling finishes. Placing web openings in double
tees allows mechanical equipment to pass through them, reducing the floor to floor height and
overall building height. The reduced building height can result in significant economy in cost
of the building envelope and in the mechanical and electrical systems. A further benefit of
weight reduction is savings in the supporting beams, columns, and foundation due to both
vertical gravity loads and horizontal seismic forces.
This paper presents the results of a research works that investigated the effect of increasing
the amount of Prestressing amount and its effective force on standard PCI double tee with web
opening. Optimization works were carried out to present a design aids using the most common
standard section in the marketing. All analysis was carried on experimental case study
considered from literatures and tested numerically by finite element method, where its already
proved that compatibility and validity of the adopted model. Herein, the research focus on
providing a tool to the users by carrying out an optimization study on prestressed double tee
beams with web opening.
2. LITERATURE REVIEW
In 1995, Kennedy and Abdalla [1] have completed a comprehensive study of beams with one
opening considering design against cracking at openings in prestressed concrete beams. They
have proposed a rather involved procedure to design for the opening; however they have not
considered simplification and possible standardization of beams with a large number of
openings. Their paper gives a good discussion of the types of cracking that can occur around
an opening in a prestressed concrete beam and how these cracks form.

Hussam Ali Mohammed
Saleh et al [2] published a two paper about the research conducted at university of Nebraska
on design of double tees with large web openings. Where the first paper dealt with experimental
and theoretical studies as well as initial design recommendations. While the second phase of
the research dealt with further maximize and standardize opening size and location.
In 1996, Savage et al. [3] tested experimentally four prestressed concrete double tee beams
with web opening under flexure, and then Hussam [4] carry a numerical investigation on the
same prestressed concrete double-tee beam using finite element modeling, to obtain the effect
of existing web opining on the behavior of such beams under flexure.
Hussam [5] also, on his PhD thesis study the behavior of prestressed concrete double tee
beam experimentally and numerically, where a program was prepared to analyze under flexure.
Results shows that the finite elements technique is a powerful method to simulate the behavior
and follow up to failure.
3. CONSTITUTIVE RELATIONSHIPS AND FINITE ELEMENT
FORMULATION
Reinforced and prestressing concrete, are usually simulated by considering the constitutive
relations of its constituents independently, because each of concrete and prestressing and
reinforcing steel have very different material properties. The 20-noded isoparametric brick
element was used to model the concrete and both prestressing and reinforcing bars was
idealized and axial members embedded within the concrete elements. The behavior of concrete
in compression was simulated by an elastic-plastic work hardening model followed by a
perfectly plastic response, which is terminated at the onset of crushing [6]. In tension, a
smeared crack model with fixed orthogonal cracks was used with the inclusion of models for
the retained post-cracking stress and reduced shear modulus. The nonlinear equations of
equilibrium were solved using an incremental-iterative technique operating under load control.
The standard and modified Newton-Raphson methods were used as solution algorithms [6].
For full details of the constitutive models and the finite element formulation adopted in this
research work can be found in reference [9]. In the present study, the computer program
3DNFEA (3-DimensionalNon-linear Finite Element Analysis)which was originally developed
by Al-Shaarbaf [6] has been used.
4. TESTED DOUBLE TEE BEAM SAMPLES
Savage test experimentally set of beams to study the effect of existing web opening on the
behavior under flexural loading up to failure. These beams were retested by Hussam [4]
numerically by using finite element method and find a good agreement between the two method
(Experimentally and Numerically). The presence of web opening was tested and set of
conclusion obtained and design charts prepared. Based on the control beam 7G1 without web
opening and another three samples with web opening, the case study was arranged. Herein, in
this study, an optimization procedure was carried on to check the effect of amount of
Prestressing strand area and its effective Prestressing force, and provide the best guide for
designing double tee beam multi-choice span length. Savage beams were prismatic members
of a typical production spanning 13.7m, where that length need to be increased. The beams
may serve as units in roofing/flooring parts or constructing parking structures.

with Web Opening
5. GEOMETRY AND SECTION PROPERTIES OF TESTED DOUBLE
TEE BEAMS
All beams tested was use in office construction, therefore the used loading was an office live
loading of 245kg/m2
plus a 100kg/m2
superimposed dead load plus 122kg/m2
to present a
50mm topping. Which about 465kg/m2
total superimposed uniform service load and 730kg/m2
an ultimate load. Concrete strength between 41 and 69MPa were considered. The finite element
analysis showed that higher concrete strength of fc
’
=48MPa and fci
’
=38MPa was required. The
final opening size used was 300×900mm based on the limitation of flexural cracking ACI 318-
02 sec. 7.7.3.2. [7]. five openings between depression points where created. And another
additional opening was placed at each end of the tee outside of the depression points.
The fabrication of tees and location of indicated positions for replacing concrete were
shown in Fig. (1), where Tee 7G1 was design as a solid tee in order to compare the behavior
to the modified tees Tees 7G2, 7G3, and 7G4 each had seven replacement locations as shown
in Fig. (2). the test specimens were identical except for additional reinforcement around the
web openings. The specimens had five 12mm diameter 1860MPa prestressing strands; four
were depressed at the one-quarter points, and the fifth strand was placed 550mm above the
bottom of the tee and was not depressed. Because the prestressing bed has holes already drilled
in it at a fixed spacing of 600mm on center for the depression device, the location of the
depression points may be 300mm away from where they designed. Same technique adopted by
Hussam [8] for strengthen the location of web openings. All shear reinforcement used in the
finite element model by Hussam [8] where repeated herein, and same technical data used. The
chosen segment was modeled using the 20-node isoparametric hexahedral brick elements. This
quarter was discretized into 74 brick elements, considering the advantage of geometric and
loading symmetry, where a segment which represents one quarter of the beam has been used
in the finite element analysis.
All specimens used within the same model adopted by Hussam [4], and loaded within the
same test procedure by using equivalent nodal loads distributed at top face of the flange.
The modelled concrete used Young’s modulus equal 27600 N/mm2
, and Compressive
strength fc’ equal 48MPa, at the same time the Tensile strength ft considered 4.1MPa, and
Poisson’s ratio, ν =0.2. While for Prestressing tendons the Young’s modulus used 200GPa,
and the Effective prestressing stress considered 950MPa and the Yield stress equal to 1860MPa
The finite element analyses have been generally carried using the 27-point rule, with a
convergence tolerance of 4%. The modified Newton-Raphson method in which the stiffness
matrix is updated at the second iteration of each increment of loading has been adopted as a
nonlinear solution algorithm. Non-uniform increments have been used for applying the external
loads. Large increments were used at the first five stages of loading, and then appreciably
smaller increments were used for stages close to ultimate load.

Hussam Ali Mohammed
Figure (1) Precast section dimensions and prestressing details [4].

with Web Opening
Figure.(2).Savage et al. beam – Reinforcement Detail of specimens .
6. BEAMS- RESULTS OF ANALYSIS
Hussam [4] predict the full behavior of the tested experimentally beams and moment-deflection
curves were plotted for all of the tees by using the finite element techniques. Good agreement
on the overall results between the finite element method and the experimental test to matching
the behavior of double tee beams with web opening under flexure.
6.1. Effect of increasing effective Prestressing force
The effect of increasing the effective Prestressing force on the behavior of the double tee beams
was predicted as shown in Fig. (3-6) and review in Table (1)
Table (1). Numerical results for the moment carrying capacity
Effective Prestressing stress(MPa)
Numerical Results
fse=950 fse=1050 fse=1150 fse=1250 fse=1350
7G1
Cracking Moment (kN-m) 40 42 45 47 50
Ultimate Moment (kN-m) 340 358 362 370 390
7G2
7G3
7G4

Hussam Ali Mohammed
Figure. (3). 7G1- mid-span moment-deflection
behavior.
behavior.
behavior.
behavior.
It’s appear the matching at the first stage of loading where the section behave as uncracked
section, where both the numerical and experimental responses are very close within the elastic
stage.
For the sold sample 7G1 without web opening, the cracking moment capacity increased by
25% within increase the effective prestressing force by 40%. The increase seems to be
incrementally with same rate. All over the stage before cracking the behavior stay almost the
same within the increase of effective prestressing force. After cracking stage up to the ultimate,
the variation start to be more effective and clearly appear. About 14% increased the ultimate

with Web Opening
moment capacity for the 40% increases in the effective prestressing force. Also, the section
show improvement on its ductility, where its allow more deflection reached to 44% more than
the original control beam.
For beams with web opening 7G2, 7G3, and 7G4, the behavior at the elastic uncrack stage
of loading almost the same with the solid beam 7G1. The development in the cracking moment
varied between 50%-78%. While the ultimate moment have more effected by the increasing
the prestressing force and its value reached 66% improvement in the moment carrying capacity,
with more ductility varied between 10%-42%.
The effect of increasing the Prestressing force was clearly shown at plastic regain its start
effect the performance. Improving behavior with higher moment capacity is the general view
of all tested samples.
6.2. Effect of changing the amount of Prestressing
For considering the effect of changing the amount of Prestressing in both (decreasing and
increasing), the tested beams were studied and variation of its moment capacity draw as shown
in Fig.(7-10), and reviewed in Table (2)
Table (1). Numerical results for the moment carrying capacity
Effective Prestressing stress(MPa)
Numerical Results
3#12 4#12 5#12 6#12 7#12 8#12
7G1 Ultimate Moment (kN-m) 275 315 340 385 415 585
behavior.
behavior.

Hussam Ali Mohammed
behavior.
behavior.
The behavior of the solid double tee beam, shown in Fig. (7) Is effected by changing the
amount of prestressing, where that studied by taking a range of the possibility of inserting
prestressing tendons in the web. The range start from (3#12 up to 8#12). The control beam had
prestressing equal to 5#12, and all the numerical beam tested compare with its full behavior.
Reducing the amount of prestressing predict brittle response, where the beam shows cracking
over all its section at early stages and fail within short time.
The ultimate moment on the control beam 7G1 reduced by 20% just by reducing two
tendons while its increased by 22% by increasing two tendons, and the improvement jumped
to 72% increased with more additional tendons. After cracking stage the beam with 8#12 show
high performance comparing with all other cases, with allowing more deflection regarding to
the control beam.
The behavior of beams with web opening follow the general pattern of the control beam,
but its effected more on the cases where tendons reduced. The beams 7G2, 7G3, and 7G4 shows
earlier cracking and reach its maximum moment capacity before the control beam reach its
cracking moment. These beams reduced its ultimate moments by 61%, 65%, and 61.5% for
reducing two tendons, while its show improvement reach 16%, 33%, and 34% when increasing
two tendons. Also, the improvement in ultimate moment jumped when increasing more one
tendons to reach 59%, 65% and 81%. Same indication for increasing the ductility by allowing
more deflection with higher moment applied.
For beam with more tendons compare with the control beam, the cracks start at the corners
of the opening and propagate on the maximum stresses due to flexural loading. all beams with
web opening failed by flexure and cracks separate from bottom to top at mid-span and first
quarter from the support.

with Web Opening
7. SPAN-LOAD CHARTS FOR PRESTRESSED CONCRETE DOUBLE
TEE BEAMS
Design aids are prepared for give a handy help for simple and fast design of prestressed double
tee beams under flexural service and ultimate loads, by carrying our a huge number or computer
runs that take much time. Curves are classified and presented considering the most common
typical sections of the double tee beam.
7.1. Description of the chosen beam
All beam tested numerically was follows the dimensioning shown in Fig. (11), where its length
taken to be from 6m to 45m span. The function of the double tee member in practice is almost
as either floor or roof, that limit the type of loading on be uniform distributed over the full span.
On that base all loading obtained from these data are considered uniformly distributed and the
support condition is fixed to the pin-roller case. Normal concrete with unit weight 23.5
kN/m3.5 and compressive strength equal to 45MPa used over all beams. Various amount of
prestressing number of tendons used as a case number one, and various value of effective
prestressing force adopted for case number two.
Figure. (11). Section dimensions (all dimension in mm).
7.2. Design Charts
First, one may consider a span length of about 6m with the above characteristics, to start the
design and recheck process by using the finite element method and in each time a various value
of effective prestressing force checked and also rechecked for various amount of prestressing
number of tendons. Considering all data adopted and listed in Hussam [4], specially the layout
of additional reinforcement. Because within the increase of span length, more wire strand need
and addition overall effective stand force must be applied.
Load Tables included herein were derived from computer-calculated data, are intended as
aids to preliminary sizing, and must be interpreted using sound engineering judgment. Each of
the series of beams tested numerically and used n creating the span-service load charts, has
been designated in three samples, (flange width-overall depth-with topping or without). For
example; beam designated as 240-60 means that it has a flange of 2400mm and an overall depth
equal to 600mm, without topping. The span-service load charts are summarized on Fig.(12-13)
with each different case.

Hussam Ali Mohammed

with Web Opening
Figure. (12). Design charts for precast prestressed double tee with web openings with various effective
prestressing force.

Hussam Ali Mohammed

with Web Opening
Figure. (13). Design charts for precast prestressed double tee with web openings with various
prestressing amount.

Hussam Ali Mohammed
NOTE THAT:
The Span-Load Tables were developed in accordance with the provisions of the "Building Code
Requirements for Reinforced Concrete", ACI 318-02, where in compression article[ACI 318-
02, Section 18.4.2(a) [7]] was considered while in tension the article [ACI 318-02, Section
18.4.2(b) [7]] is considered.
Additional references on ( [8], [9], [10], [11], [12], and [13]) where double tee beam were
investigated experimentally and numerically.
7. CONCLUSIONS
1. Overall the three phases of study, the finite element method prove that its could be
a powerful tool to simulate the full behavior of prestressed concrete double tee
beams with web openings under flexure, and could be a good laboratory to carry
huge number of tests with several parameter that could improve the performance of
the new beams.
2. This research focus on the prestressing tendons, where the variation of its value and
the applied effective prestressing force are studied. In general, It’s appear the
matching at the first stage of loading where the section behave as uncracked section,
where both the numerical and experimental responses are very close within the
elastic stage.
3. The cracking moment capacity increased by 25% within increase the effective
prestressing force by 40% for the sold sample 7G1 without web opening. The
increase seems to be incrementally with same rate. After cracking stage up to the
ultimate, the variation start to be more effective and clearly appear. About 14%
increased the ultimate moment capacity for the 40% increases in the effective
prestressing force. Also, the section allow more deflection reached to 44% more
than the original control beam.
4. For beams with web opening 7G2, 7G3, and 7G4, the behavior at the elastic uncrack
stage of loading almost the same with the solid beam 7G1. The development in the
cracking moment varied between 50%-78%. While the ultimate moment have more
effected by the increasing the prestressing force and its value reached 66%
improvement in the moment carrying capacity, with more ductility varied between
10%-42%.
5. The ultimate moment of the control beam 7G1 reduced by 20% just by reducing
two tendons while its increased by 22% by increasing two tendons, and the
improvement jumped to 72% increased with more additional tendons.
6. The behavior of beams with web opening follow the general pattern of the control
beam, but its effected more on the cases where tendons reduced. The beams 7G2,
7G3, and 7G4 shows earlier cracking and reach its maximum moment capacity
before the control beam reach its cracking moment.
7. beams 7G2, 7G3, and 7G4 reduced its ultimate moments by 61%, 65%, and 61.5%
for reducing two tendons, while its show improvement reach 16%, 33%, and 34%
when increasing two tendons. Same indication for increasing the ductility by
allowing more deflection with higher moment applied.
8. For beam with more tendons compare with the control beam, the cracks start at the
corners of the opening and propagate on the maximum stresses due to flexural
loading. all beams with web opening failed by flexure and cracks separate from
bottom to top at mid-span and first quarter from the support.

with Web Opening
9. By get the benefit from the Finite element technique a large number of computer
runs was made to produce curves that give a handy help for simple and fast design
of prestressed double tee beams under flexural service and ultimate loads, where
the designer have a wide range of variety upon choosing the value of prestressing
tendons area and its effective applied force.
REFERENCES
[1] Kennedy, John, B., and Abdalla Hany, “Design Against Cracking at Openings in
Prestressed Concrete Beams,” PCI JOURNAL, V.40, No.6, Nov-Dec 1995, pp.60-75.
[2] Selah M., Tadros K., Einea A., and Fischer, L, “Standardized Design of Double Tees With
Large Web Openings", PCI Journal, Nov-Dec 1999.
[3] Savage, M., Tadros, K., Panchy Arumugasaamy, Fischer, L, “Behavior and Design Double
Tees with Web Openings”, PCI JOURNAL, V.87, No.8, Jan-Feb. 1996
[4] Hussam Ali Mohammed, "The Effect of Web Opening on Prestressed Concrete Double Tee
Beams under Flexure", The Second Annual Scientific Conference of the College of
Engineering /Babylon University, Iraq, 24-25 March 2010.
[5] Hussam A. Mohammed "Experimental and Nonlinear Analysis of Non-Prismatic Double
Tee Prestressed Concrete Beams" PhD Thesis, Baghdad University, Sep. 2005.
[6] Al-Shaarbaf, I. A. S., “Three-dimensional nonlinear finite element analysis of reinforced
concrete beams in Torsion”, Ph.D. Thesis, University Of Bradford, 1990.
[7] ACI-Committee 318, " Building Code Requirements for Structural Concrete (ACI 318M-
95) and Commentary (ACI 318RM-95) ", American Concrete Institute, Detroit, Michigan,
2002.
[8] Hussam Ali Mohammed, "Nonlinear Analysis of Flanged Reinforced Concrete Beams
Using Three-Dimensional Finite Element Model", MSc Thesis, Saddam University, 2000.
[9] Hussam Ali Mohammed, Ihsan A. Shaarbaf, Khild S. Mahmod, " Finite Element Analysis
of Prestressed Concrete Double Tee Beams", Journal of Babylon University for
Engineering Science, Vol.12, No.5, 2006.
[10] Hussam Ali Mohammed, "Behavior of Prestressed Concrete Non-Prismatic Double Tee
Beams", Journal of Kerbala University, Vol.8, No.1, 2010.
[11] Hussam Ali Mohammed, "Finite Element Analysis of Non-Prismatic Prestressed Concrete
Double Tee Beams" Journal of Kerbala University, Vol.8, No.1, 2010.
[12] Hussam Ali Mohammed, "Analysis and Design of Precast Concrete Structures”, 1st
Addition Book, ISBN: 978-9922-20-146-7, 2018.
[13] Hussam Ali Mohammed, "Analysis and Design of Prestressed Concrete Structures”, 1st
Addition Book , ISBN: 978-9922-20-145-0, 2018.

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