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Design of Reinforced Concrete Beams With Openings

Authors:
Waleed E. El-Demerdash at Mansoura University
Waleed E. El-Demerdash
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Abstract and Figures

Ordinary beams with openings and deep beams with and without openings are considered disturbed regions where their strains within any section are significantly nonlinear. Therefore, it is not adequate to design those regions using either bending theory or conventional shear design equations. Hence, it is essential to rely on a rational method such as the strut-and-tie model. The behavior of experimentally tested reinforced normal- and high- strength concrete simply supported shallow beams (with and without openings) and simple and continuous deep beams (with openings) was studied. In this study, the Strut-and-Tie Models STM for all such selected beams are suggested based on the available experimental results of crack patterns, modes of failure, and internal stresses trajectors obtained from elastic finite element analysis. The obtained STM results are compared with test results. To draw a complete picture of the response of the studied beams, a 3D nonlinear finite element analysis is conducted. From which, the output results of cracking patterns, deflections, failure mode and strain and stress distributions (that can not be obtained using the strut-and-tie model) are obtained. In addition, a full design procedure along with numerical examples, reinforcement detailing, and design recommendations for beams with openings only is presented.
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... Concrete was modeled using a three dimensional element called SOLID65 which is capable of crushing in compression and cracking in tension. It has eight nodes with three translational degrees of freedom (x, y, and z) for each node, Waleed EL-Demerdash [40] listed other characteristics of the mentioned element. ...
... Using a work done by Waleed El-Demerdash [40] as a basis, materials models for SOLID65, LINK180, and SOLID185 were defined as illustrated in Table (5-1). ...
EFFECT OF EXTERNAL PRESTRESSING ON BEHAVIOR OF HIGH STRENGTH REINFORCED CONCRETE BEAMS WITH OPENINGS
Thesis
Full-text available
  • Feb 2021
External prestressing has been proven technically attractive and economic in constructing new bridges and retrofitting aged ones that need strengthening. High strength concrete (HSC) has been also more widely spread than the past and became more and more frequently required in constructions because of enormous development in material technology. Openings in concrete elements are a facility which utility services pass through. Although combining the effect of external prestressing and openings on concrete elements is very important, data in this field suffered from a hard lack. So, the current work aims at providing some data on the combined effect of external prestressing and openings on HSC beams. This can offer an additional level of fascination and innovation for constructions. For this aim, seven externally prestressed rectangular HSC beams with variable central web openings, including a reference solid beam, were loaded incrementally to failure in order to study their behavior. All the beams (with the same dimensions, reinforcement ratio (ƿ), but variable opening size) were externally prestressed with the same force. A three-dimensional nonlinear finite element analysis based on ANSYS-19.2 was carried-out to examine the accuracy of the experimental results. After that, ANSYS-19.2 was used to obtain failure loads for beams tested previously by other researchers. It was also used for modeling seventy externally prestressed HSC beams with central web openings and obtaining their failure loads. Finally, based on the obtained results, a general formula was proposed to compute the failure loads of externally prestressed HSC beams with central web openings.
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... It has eight nodes with three translational degrees of freedom (x, y, and z) at each node, Fig. 8. The following basic assumptions should be considered in the element formulation El-Demerdash [25]: ...
... Mathematical representation of the stress-strain curve of concrete in compression was used. Based on El-Demerdash [25], material models were defined as shown in Table 8. ...
EFFECT OF EXTERNAL PRESTRESSING ON BEHAVIOR OF HIGH STRENGTH REINFORCED CONCRETE BEAMS WITH OPENINGS STRUCTURAL ENGINEERING EFFECT OF EXTERNAL PRESTRESSING ON BEHAVIOR OF HIGH STRENGTH REINFORCED CONCRETE BEAMS WITH OPENINGS EFFECT OF EXTERNAL PRESTRESSING ON BEHAVIOR OF HIGH STRENGTH REINFORCED CONCRETE BEAMS WITH OPENINGS
Thesis
Full-text available
  • Feb 2021
External prestressing has been proven technically attractive and economic in constructing new bridges and retrofitting aged ones that need strengthening. High strength concrete (HSC) has been also more widely spread than the past and became more and more frequently required in constructions because of enormous development in material technology. Openings in concrete elements are a facility which utility services pass through. Although combining the effect of external prestressing and openings on concrete elements is very important, data in this field suffered from a hard lack. So, the current work aims at providing some data on the combined effect of external prestressing and openings on HSC beams. This can offer an additional level of fascination and innovation for constructions. For this aim, seven externally prestressed rectangular HSC beams with variable central web openings, including a reference solid beam, were loaded incrementally to failure in order to study their behavior. All the beams (with the same dimensions, reinforcement ratio (ƿ), but variable opening size) were externally prestressed with the same force. A three-dimensional nonlinear finite element analysis based on ANSYS-19.2 was carried-out to examine the accuracy of the experimental results. After that, ANSYS-19.2 was used to obtain failure loads for beams tested previously by other researchers. It was also used for modeling seventy externally prestressed HSC beams with central web openings and obtaining their failure loads. Finally, based on the obtained results, a general formula was proposed to compute the failure loads of externally prestressed HSC beams with central web openings.
View
... Concrete was modeled using a three dimensional element called SOLID65 which is capable of crushing in compression and cracking in tension. It has eight nodes with three translational degrees of freedom (x, y, and z) for each node, Waleed EL-Demerdash [40] listed other characteristics of the mentioned element. ...
... Using a work done by Waleed El-Demerdash [40] as a basis, materials models for SOLID65, LINK180, and SOLID185 were defined as illustrated in Table (5-1). ...
View
... It has eight nodes with three translational degrees of freedom (x, y, and z) at each node, Fig. 8. The following basic assumptions should be considered in the element formulation El-Demerdash [25]: ...
... Mathematical representation of the stress-strain curve of concrete in compression was used. Based on El-Demerdash [25], material models were defined as shown in Table 8. ...
Experimental and numerical study on the performance of externally prestressed reinforced high strength concrete beams with openings
Article
Full-text available
  • Jan 2021
This study investigates experimentally and numerically the performance of externally prestressed reinforced high strength concrete (HSC) beams with central openings. Seven externally prestressed rectangular HSC beams (six with central openings and a reference solid beam) are loaded incrementally to failure. All the beams have the same dimensions, reinforcement ratio and openings of variable size. Experimentally, the results show that, the appearance of the first flexural crack and the flexural stiffness reduction are largely governed by opening height. In contrast, the opening length greatly affects the presence of the first shear crack and the obtained values of strains in stirrups. Additionally, the opening length and height when combined can affect the strains in top- and bottom-bars and the failure load of the teste beams. Numerically, a three-dimensional nonlinear finite element analysis using ANSYS has been carried-out to analyze seventy (70) externally prestressed HSC beams with central openings. Based on the numerical results, a general formula to predict the ultimate moment is generated and verified. It can be used to predict the load carrying capacity of aging concrete elements with openings retrofitted using external prestressing techniques.
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... Transversal openings in reinforced concrete beams have gained significant popularity in recent decades due to their numerous advantages. These openings provide flexibility for accommodating building services and facilitate their passage through beams, offering customizable shapes and sizes [1,2,3,4,5]. Furthermore, they contribute to cost savings by reducing storey heights and self-weight dead loads, while their implementation requires minimal effort. ...
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... Also, passing utility services through openings in the floor beam webs might minimize the required storey height and encourages the designers to reduce the height of the structure which leads to more cost-effective design. Including transverse openings in the web of a reinforced concrete beam results in unexpected changes in the dimensions of the cross section of the beam and hence, the corners of the opening would be subjected to stress concentration and it is may induce transverse cracks in the beam [3]. So, the effect of openings on the strength and behavior of reinforced concrete beams must be considered and the design of these beams needs special concern. ...
VALIDATION OF FINITE ELEMENT MODELING FOR RECTANGULAR REINFORCED CONCRETE BEAMS WITH WEB OPENINGS
Article
Full-text available
  • May 2019
The present paper aims to validate ABAQUS finite element model to analysis the rectangular reinforced concrete beams in order to study web opening effect on the shear, and ultimate strength of these beams. The validation has been achieved through comparison of load-- deflection curves obtained from the finite element model with those of experimental works of another researcher. The dimensions and flexural reinforcement of the beams were kept the same. The investigated test parameters were the size and the location of the openings. Comparison between load-deflection curves obtained from finite element model with those of experimental works indicates good agreement such that the proposed model can be adopted in future for further studies.
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An experimental investigation to determine the failure load of optimal hammer head pier cap and interpolate using univariate splines machine learning algorithm
Article
  • Jan 2023
The application of structural optimisation is fast changing the thinking of Design Engineers. With the rapid development in high strength concrete and other materials which can resist higher loads, the task of reducing the weight of the structure can be addressed with ease. The present study is an application of topology optimisation of continuum structures. The design domain is modelled using first order basis splines and optimisation is performed using optimality criteria minimising strain energy as the objective function. A model pier cap is chosen with the standard dimensions of 3 feet x 9 in x 4 in. The size and location of openings are determined using topology optimisation and drawn in AutoCAD® software. The casting is done using concrete with different percentages of replacement of cement and fine aggregate. Cement is partially replaced using Alcofine and fine aggregate is partially replaced using waste foundry sand. The foundry sand is an industrial waste obtained from the foundry industry located at Balanagar, Hyderabad. Four specimen beams are cast and tested in the laboratory. Steel fibres are used to care for the tensile stresses produced within the beam. The analysis done here can be applied to any material other than concrete as well. The failure load is determined in the laboratory for each sample. The interpolation of failure load is done using python code and run on Anaconda Jupyter ® platform to determine the value of failure load for any percentage of replacement between 0 to 10%.
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Towards the Consistent Design of Reinforced Concrete Structures.
Article
  • Apr 1984
The B-region of a structure to which theory of bending (B) is applicable are now designed accurately. On the other hand, damage accumulates in the D-regions chracaterized by structural and geometric discontinuities (D) such as load application points, abrupt changes of alignment, holes, etc. For such parts there hardly exist any proper design concepts, and although they are just as important as the parts designed for bending, they are often provided merely with 'nominal' reinforcement. A rational method, which is compatible with standard design procedure and with which the whole structure can be designed, consists in extending and generalizing the know truss models such that they comprise the whole structure, with uniform design of all the tensile and compressive members of the models, including the nodal joints.
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Shear behavior of steel fiber high-strength reinforced concrete continuous beams
Article
  • May 2002
In this paper the shear behavior of steel fiber high strength reinforced concrete continuous beams was studied. A series of ten continuous beams were fabricated and tested to failure under two concentrated loads in order to investigate the effect of several important parameters on the shear behavior of such type of beams. These parameters included: the steel fiber volume content and the shear span to depth ratio. For all tested beams the initiation of cracks and its propagation was observed and recorded. Deflections and steel strains were measured thus load-deflection and load-strain relationships were detected. Also, failure loads and failure modes were observed for all tested beams. Test results have revealed the beneficial effects of the inclusion of steel fibers in the enhancement of shear behavior of high strength concrete continuous beams. The presence of steel fibers significantly enhanced the post cracking tensile strength of concrete and therefore the shear strength of continuous beams was improved. Also, it was found that the brittle nature of failure in the case of high strength concrete continuous beams was transformed into a more ductile one for beams containing steel fibers. Finally, the experimental results for shear strength of tested continuous beams were compared to theoretical predictions from empirical equations found in the literature for the estimation of shear strength of simply supported steel fiber high strength concrete beams.
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Experimental evaluation of strut-and-tie model applied to deep beam with opening
Article
  • Jan 2000
  • ACI STRUCT J
Where geometric discontinuities exist in structural concrete members, current code documents provide little direction for design. The design of these unusual members can be better understood by using the strut-and-tie model. Combinations of two distinctly different strut-and-tie models were used to design four deep beams each with a geometric discontinuity in the form of a large opening. This paper describes the performance of four physical models that were constructed based on these varied designs. The deep beams were simply supported and tested using a point load. Each of the four beams resisted considerably more than the factored design load. This successful test series reveals the power, versatility, reliability, and predictability of the strut-and-tie modeling technique.
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Tests on reinforced concrete deep beams
Article
  • Feb 2007
Reinforced concrete deep beams are commonly used in structures as load distribution elements, such as transfer girders, pile caps, folded plates, and foundation walls. These members frequently have several supports and web openings to facilitate essential services.
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Evaluation of minimum shear reinforcement requirements for higher strength concrete
Article
  • May 1999
  • ACI STRUCT J
This paper presents an evaluation on the minimum shear reinforcement requirements given in the ACI, Canadian, and Turkish codes for high-strength concrete. Thirteen beams having the minimum shear reinforcement required by ACI 318-83, the Turkish Code, and the equations proposed in this paper were tested. Concrete strength varied between 60 and 80 MPa (8700 and 11,600 psi). For high-strength concrete (f′c > 69 MPa), the minimum shear reinforcement requirements of the Turkish Code and ACI 318-95 are not very different from one another. Similarly, requirements of the 1994 Canadian Code (CSA A23.3-94) are not too different from the proposed equation. In light of the test results, the adequacy of code requirements are discussed. Emphasis is given to reserve strength, ductility, and cracking.
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Shear strength of reinforced high-strength concrete deep beams
Article
  • Mar 2001
  • ACI STRUCT J
Fifty-three reinforced concrete deep beams with compressie strengths in the range of 23 MPa ≤ f c′ ≤ 74 MPa (3335 psi ≤ f c′ ≤ 10,730 psi) were tested to determine their diagonal cracking and ultimate shear capacities symmetrically under two-point loading. The effective span-depth ratio l e/d was varied from 3.0 to 5.0, and the shear span-effective depth ratio a/d from 0.5 to 2.0. All the beams were singly reinforced with ratio pt of 0.0129, 0.0156 and ratio of ρ v from 0 to 0.0034, and ρ h from 0 to 0.0094, respectively. The ultimate shear failure mode of deep beams was governed by a/d regardless of concrete strength. At a lower a/d, deep beams with high-strength concrete failed abruptly without any caution, which could be seen in deep beams with normal-strength concrete. Test results indicate that the ultimate shear strength of deep beams was determined predominantly by a/d. For all tested beams, ACI Code Eq. (11-29) and (11-30) are conservative and underestimate the effect of concrete compressive strength f c′ and that of longitudinal steel reinforcement ρ t in deep beams using high-strength concrete. Addition of horizontal shear reinforcement does not improve the ultimate shear strength with decreasing a/d in deep beams with high-strength concrete.
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High-strength concrete deep beams with effective span and shear span variations
Article
  • Jul 1995
Nineteen reinforced concrete deep beams with compressive strengths in the range of 41 MPa ≤ fc′ ≤ 59 MPa (6000 psi ≤ fc′ 8600 psi) were tested under two-point top loading. All the beams were singly reinforced with main steel percentage ρ = 1.23 percent and with nominal percentage of shear reinforcement ρv = 0.48 percent. The beams were tested for seven shear span-depth ratios a/d, ranging from 0.27 to 2.70, and four effective span-depth ratios le/d, ranging from 2.15 to 5.38. Test results indicate that le/d has little influence on the magnitude of the failure load. But for beams with a/d ≥ 1.00, the flexural failure mode becomes dominant with increasing led. The test results are compared with predictions based on the current ACI Building Code. The comparisons reported in this paper will provide an added assurance to designers that the deep-beam provisions in the ACI code, though essentially based on concrete strengths of less than 41 MPa (6000 psi), will insure safe designs for higher strength deep beams. However, the ACI code tends to be rather conservative, as shown by comparison to the Deep-Beam Design Guide issued by the Construction Industry Research and Information Association, London. Nevertheless, the ACI code has the important advantage of being easy to use.
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Minimum transverse reinforcement fo bottle-shaped struts
Article
  • Nov 2006
  • ACI STRUCT J
Strut-and-tie modeling involves the use of struts to model the flow of compression within a concrete member. Bottle-shaped struts are wider at their midpoint than at either end. As the struts widen near the midpoint, tensile stresses transverse to the direction of compression are developed. Reinforcement must be placed within the strut to carry the transverse tension. This paper presents an equilibrium-based approach to determining the necessary amount of transverse reinforcement for a bottle-shaped strut. A database of 476 test specimens was then used to evaluate the equilibrium-based equations along with a series of three tests of deep beams. The strut efficiency factors presented in Appendix A of ACI 318-05 were used. in this evaluation. Current ACI 318-05 provisions allow the design of a deep beam without any shear reinforcement; this issue is highlighted and its shortcomings are discussed.
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Effects of creating an opening in existing beams
Article
  • Nov 1999
  • ACI STRUCT J
Nine T-beams were fabricated with circular openings through the web to simulate drilling of holes in an existing beam either for the passage of service ducts or for the determination of in place concrete strength. The major parameters considered in the study were the size and location of openings. These beams were tested to failure. Test results indicate that an opening, when created near the support region of an existing beam, leads to early diagonal cracking and significantly reduces the strength and stiffness of the beam. Also, irrespective of the size and location of the opening, the serviceability limit state of cracking may be seriously affected. Filling the opening (created for the determination of in place concrete strength) by nonshrink grout is not adequate to restore the original response. Therefore, when such openings are unavoidable, adequate measures should be undertaken to strengthen the beam so as to retain the degree of safety and serviceability considered in the original design. It has been shown that the weakness introduced by creating an opening may be completely eliminated by employing a suitable strengthening method.
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Tests of reinforced concrete continuous deep beams with web openings
Article
  • May 2000
  • ACI STRUCT J
Test results of 16 reinforced concrete two-span continuous deep beams with web openings are reported. All test specimens had the same geometry and main longitudinal top and bottom reinforcement. The main parameters considered were the size and position of the web openings, and web reinforcement arrangement. Two modes of failure were observed, depending on the position of the web openings. For beams having web openings within interior shear spans, the failure is developed by diagonal cracks between the web opening corners and the edges of the load and central support plates. For beams having web openings within exterior shear spans, the mode of failure is characterized by major diagonal cracks within interior and exterior shear spans. The diagonal cracks that occurred in the interior shear span extended to join the edges of the load and central support plates, and at the same time, the diagonal cracks that formed at the web opening corners propagated both ways towards the edges of the had and end support plates. Web openings within interior shear spans caused more reduction on the beam capacity than those within exterior shear spans. The vertical web reinforcement had more influence on the beam capacity than the horizontal web reinforcement. An upper-bound analysis of the two failure mechanisms that occurred in the experiments is introduced, and design equations are developed.
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