Guray Arslan

Cracking shear strength of RC slender beams without stirrups

Abstract This study presents alternative cracking shear strength equations for slender reinforced concrete (RC) beams without stirrups. More than 80 data has been obtained from existing sources of RC beam shear test results covering a wide range of beam properties and test methods. The proposed cracking shear strength equations are applied to existing test data for normal strength concrete (NSC) and high‐strength concrete (HSC) slender beams and the results are compared with those predicted by the ACI 318 equations. It can be also noted that the test results are in better agreement with proposed cracking shear strengths. However, because the test data for high‐strength concrete members are very limited, further research is required to verify these equations.

Diagonal Tension Failure of RC Beams Without Stirrups

Abstract The shear failure of reinforced concrete beams is one of the fundamental problems in civil engineering; however, the diagonal tension strength of reinforced concrete (RC) beams without stirrups is still in question. This paper focuses on the prediction of diagonal cracking strength of RC slender beams without stirrups. In slender beams, flexural cracks develop in the tension zone prior to a diagonal cracking. Using the basic principles of mechanics, but cracking included, and theory of elasticity, a diagonal cracking strength equation is proposed for both normal and high strength concrete beams. The proposed equation, the requirements of six codes of practice and seven equations proposed by different researchers are compared to the experimental results of 282 beams available in the literature. It is found that the predictions from the proposed equation are in good agreement with the experimental results.

CONTRIBUTION OF CONCRETE TO SHEAR STRENGTH OF RC BEAMS FAILING IN SHEAR

Reinforced concrete (RC) beams with light transverse reinforcement are vulnerable to shear failure during seismic response. In order to prevent brittle shear failures at beam plastic hinge regions of earthquake-resistant structures, the Turkish Earthquake Code and ACI318 require the use of sufficient transverse reinforcement to resist the total expected shear demand. These codes tend to be excessively conservative and, in some cases, the contribution of the concrete to the shear strength is neglected. The aim of this study is to investigate the contribution of concrete to shear strength of RC beams failing in shear experimentally. The beams were tested under monotonically increasing reversed cyclic loading to determine the concrete contribution to shear strength. It is observed that the concrete contribution to the shear strength at ultimate state ranges from 18% to 69% of the ultimate strength.

Nonlinear analysis of RC columns using the Drucker-Prager model

Abstract This paper aims to investigate the correct prediction of load carrying capacity of reinforced concrete (RC) columns. Although substantial experimental and analytical researches have been conducted to model and simulate the response of concrete, little success has been achieved for the general description of the failures of RC columns subjected to bending and axial load. In order to predict the load carrying capacity of RC column, this paper introduces a new relationship for calculating the cohesion parameter of Drucker-Prager criterion. The relationship is developed from a parametric study of a large number of nonlinear finite element analyses of RC columns to account for the parameters. Incorporating these parameters into the failure criterion of concrete, the failure cone of Drucker-Prager model is enforced to approximate and coincide with the whole compressive meridian of the criterion up to the analytically predicted point of the load carrying capacity in the failure analyses. The proposed ap...

Use of Post-tensioned Concrete Slabs for Sustainable Design of Buildings

Post-tensioned concrete design can lead to considerable savings in materials, construction time and future maintenance costs, compared to the conventional reinforced concrete design. Pre-stressing improves the behaviour of concrete in tension. Thus, for the same imposed load, a more slender structure can be designed. Reduced slab depth results in reduced building height and savings in related building components. These savings translate into less material usage which means reduced embodied energy for a structure thus, creating a sustainable solution. In this study, buildings with post-tensioned and conventional reinforced concrete slab systems are compared. Two buildings with the same floor plans are designed using reinforced concrete and post-tensioned slab systems. The span length is chosen as 6.5 m, which is a practical limit for a relatively economical reinforced concrete solution. The buildings are designed as 10, 20 and 40 stories to demonstrate the change in material savings as the number of floors increases. Since post-tensioned slabs can be designed thinner for the same loads and spans, total weight of the structure reduces and this results in smaller columns, lower seismic loads and foundation loads. The results showed that the difference in steel material savings between conventional and post-tensioned solutions increases as the number of floors increases. It is concluded that incorporating post-tensioning into common design practice not only reduces construction costs but also reduces embodied energy by using less material and produces a sustainable structural design.

Shear degradation of reinforced concrete beams

Reinforced concrete (RC) members are designed to have shear strengths much greater than their flexural strengths to ensure flexural failure according to the current design codes. Flexure failure in beams starts with flexural yielding and shear degradation in the lateral load capacity occurs due to damage related to flexural deformations. Because of the complexity of shear strength degradation, seismic codes tend to be excessively conservative and do not take into account, the contribution of concrete in certain cases. The research described in this paper proves numerical information about the effect of flexure on the shear degradation of RC beams. An analytical equation reflecting the reduction in concrete contribution to shear strength is investigated. It is also observed that the contribution of concrete to shear strength is decreased by an increase the ratio of the shear strength to transverse load capacity calculated from flexural capacity.

Influence of Polypropylene Fibers on the Shear Strength of RC Beams Without Stirrups

Reinforced concrete (RC) beams with light transverse reinforcement are vulnerable to shear failure during seismic response. The codes require the use of a certain amount of transverse reinforcement to resist the expected total shear demand to prevent brittle shear failure at plastic hinge regions. Some codes ignore the contribution of concrete to shear strength when the shear demand due to seismic effects is above a certain level. This research studied the contribution of concrete to shear strength of beams reinforced with longitudinal bars and polypropylene fibers (PPF). The beams including two reference and two macro-synthetic polypropylene fibers reinforced concrete (PPFRC) beams tested under concentrated loads at mid-span to determine the shear strength. The variable parameters are volume fraction of polypropylene fibers (Vf) and shear span-to-depth ratio (a/d). Deflection of the beam and the cracking pattern were monitored during the test at different stages of the monotonic loading until failure. When the beams with a/d = 2.5 and 3.5 are compared, it is concluded that the contributions of PPF to the shear strength at ultimate state are 0.39 MPa and 0.34 MPa, respectively, in case of the beams with volume fractions of PPF equal to 1.0%. It is observed that the contribution of PPF to shear strength decreases with the increasing a/d. It can also be stated that the dissipated energies under the area of load-deflection curve by the PPFRC beams are 341 and 226 times the energy dissipated by a/d = 2.5 and a/d = 3.5 reference beams, respectively.

Influence of polypropylene fibres on the shear strength of RC beams with web reinforcement

Abstract The use of various types of fibres within concrete matrix for enhancing structural performances of concrete or reinforced concrete (RC) members has been gaining interest in recent years. While a considerable amount of research has been conducted for using steel fibres, the studies on the other types of fibres are limited. For the purpose of extending our knowledge on polypropylene fibres in RC beams, an experimental programme was carried out for investigating the shear behaviour of polypropylene fibre-reinforced concrete (PFRC) beams. This paper presents the results of beams with web reinforcement divided into three groups according to the shear span-to-effective depth ratio and the amount of web reinforcement. Each group consists of a reference RC beam and three beams with fibre contents of 1.0, 2.0 and 3.0%. The simply supported beams were loaded at mid-span. Experimental results show that the addition of polypropylene fibres enhanced the shear behaviour of RC beams with web reinforcement. Furthermore, an expression for the contribution of web reinforcement was derived by considering the effectiveness of web reinforcement and it was introduced to the equation proposed previously for predicting the shear strength of PFRC beams without web reinforcement. The predictions agree with the experimental results.