The construction of the three new toll bridges in California has highlighted the application of the hollow rectangular bridge piers with highly-reinforced boundary elements and the connecting walls. However, current conservative design approaches result in massive cross sections that can lead to increased construction cost. This study investigates the feasibility of defining new limits for a seldomly considered failure mode that could lead to more slender cross sections with the use of high-strength-concrete (HSC).The possibility of web crushing failure in shear dominated reinforced concrete element rises when the dimensions of the boundary elements become larger and the webs becomes thinner. Web crushing, or diagonal compression failure, manifests itself as compression failure of concrete struts formed by diagonal tension cracking in the wall web. The failure is brittle in nature and therefore, it is mandated to be suppressed for design in seismic regions. However, it is hypothesized in this study that web crushing failures may occur after significant and stable ductile response by using HSC by increasing the capacity to crushing capacity proportionally to the concrete's compressive strength. To verify the hypothesis, eight 1/5-scale cantilevered structural walls with highly confined boundary elements were tested with design concrete compressive strengths of 34, 69, 103, and 138 MPa (5, 10, 15 and 20 ksi) under cyclic and monotonic loading protocols. The experimental results revealed that HSC can effectively delay web-crushing failures and increase the displacement ductility levels of structural walls. To evaluate the seismic performance of HSC hollow bridge piers, two 1/4-scale hollow pier units, consisting of an assembly of four walls with heavily confined corner elements, were subjected to simulated seismic demands in diagonal and multi-directional directions with design concrete strengths of 34 and 138 MPa (5 and 20 ksi), respectively. Both test units exhibited stable ductile behavior until web crushing at moderate ductility levels. The comparable ductility capacities of the pier test units indicate that the advantageous effect of HSC in improving web crushing capacity is compromised by concrete damage and strength degradation under multi-directional loading.Comprehensive nonlinear finite element (FE) modeling was conducted through 3D FE analyses with plasticity-based constitutive models and 2D FE analyses with phenomenological constitutive models to enhance understanding of web crushing capacity in structural walls. The results were compared with test data at the global and local levels to evaluate the performance of analytical methods in predicting flexural and shear behavior. The analytical models revealed that the concrete stress demand at web crushing is only a small portion of the cylinder concrete compressive strength due to the complex stress state in the web crushing region. The results also confirmed that web crushing, in the form of an inelastic shear failure, is caused by flexure-shear interaction effects in the wall web. In view of the complexity and enormous efforts entailed in finite element modeling as well as the inability of the modeling approaches in capturing failure, simplified analytical method based on truss models extracted from observations of the inelastic shear cracking and failure mechanisms were implemented. This was done by modifying an existing comprehensive inelastic strut-and-tie model for assessment of web crushing capacity. Calibration of the model with experimental results showed that the modifications led to improved predictions of web crushing capacity of high-strength-concrete structural walls.
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