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

Optimal finite element size in reinforced high-strength concrete beams

Açıklık ortasında tekil yüklü betonarme kirişlerde kesme ve eğilme mukavemetleri; doğrusal olmayan (Drucker-Prager akma kriteri) çözüm yöntemleri temel alınarak deneylerle uyumlu tahmin edilebilmektedir. Bu çalışmada; kesme mukavemetini hesaplamak için kiriş ortasından tekil yükle yüklenmiş donatılı, yüksek mukavemetli beton kirişlerde, deney sonuçları ile tutarlı yük-yerdeğiştirme eğrisini veren uygun sonlu eleman boyutları araştırılmıştır. Karşılaştırmaya tabi tutulan deney serilerinde değişkenler; beton basınç mukavemeti, kesme açıklığının kiriş etkili derinliğine oranı (a/d) ve enine donatı oranıdır. Kirişler doğrusal olmayan çözümlemeye tabi tutulmuş ve sonlu eleman boyutlarının uygun değerleri araştırılmıştır.Anahtar Kelimeler: Kesme mukavemeti, boyut etkisi, yüksek mukavemetli beton, kesme donatısı oran, sonlu elemanlar.Ever since the finite element method was applied to nonlinear problems in the field of reinforced concrete, many researchers have tried to predict the shear and bending strengths of reinforced concrete beams by using various material models for concrete.  In this study; to determine shear strength of reinforced high-strength concrete beams with shear span to depth ratios between 1.5 and 2.5, under concentrated loads at midspan, finite element size effect on load carrying capacity has been investigated analytically. In order to obtain more accurate numerical solutions from the finite element simulation of the reinforced high-strength concrete beams, the beams are evaluated for the different mesh size. Providing a larger size than optimum mesh size configuration for the nonlinear analysis, the whole load-deflection behavior of the beams have been analyzed and the main results of the numerical analyses were compared with the results of reinforced high-strength concrete beams experimental results reported in literature (Shin et al. 1999) to demonstrate how accurately the present mesh size predicts the load carrying capacity. The test variables were compressive strength of concrete, the shear span to depth ratio (a/d) and vertical shear reinforcement ratio for the comparison.  The elasto-plastic analyses of the beams, employing the Drucker-Prager yield criterion for concrete, have been performed and reasonable mesh size has been investigated. Keywords: Shear strength, size effect, high-strength concrete, shear reinforcement ratio, finite element