International Concrete Abstracts Portal

The modeling of concrete constitutive relationships in cyclic compression has attracted a lot of research attention. In this study, a normalized envelope stress-strain curve made for concrete in uniaxial compression is mathematically derived. The compression loops are formulated using a bilinear unloading path followed by a linear reloading path based on thorough observations and calibrations of available experimental data. The proposed normalized model is calibrated against a set of experimental cyclic stressstrain data. This model is shown to yield robust results by proving it successful in capturing five other independent experimental cyclic stress-strain curves. This proposed model may prove valuable for the implementation and analysis of members subjected to cyclic loading in numerical finite element analysis.

Reinforced concrete walls are used commonly in low- and mid-rise construction because they provide high strength, stiffness, and durability. In regions of low and moderate seismicity, ACI 318 Code requirements for minimum reinforcement ratio and maximum reinforcement spacing typically control over strength-based requirements. However, these requirements are not well supported by research. The current study investigates requirements for the amount and spacing of reinforcement using experimentally validated nonlinear finite element modeling. For lightly reinforced concrete walls subjected to out-of-plane loading, i) peak strength is controlled by concrete cracking, and ii) residual strength depends on the number of curtains of steel. Walls with very low steel-fiber dosages were also studied. Results show that fiber, rather than discrete bars, provides the most benefit to wall strength, with fiber-reinforced concrete walls achieving peak strengths more than twice that of identically reinforced concrete walls.

This paper examines the inaccuracy of the initial strain method that is generally adopted in 3D finite element prestressing analysis and discusses the merits of a newly developed method to calculate 3D prestressing effects. The new method considers friction loss of the tendon force as well as pseudo-centripetal forces, allowing a wide range of functional forms for the prestressed concrete (PC) steel force distribution assumption. This study examined the basic concepts for adopting the functional form of the PC steel force distribution at the prestressing and seating stages, after which the observed and calculated values of pulled-out lengths of PC steel were compared to assure the credibility of the assumed functional form of the PC steel force distribution. A three-span continuous bridge model was used to compare results obtained by the conventional method and the new 3D method. The equilibrium of a free body was used also to evaluate the accuracy of results by the new method. The importance of the new method being able to calculate a pulled-out PC steel length considering concrete deformation was stressed because this value may be adopted to confirm assumptions of the PC steel force distribution.

The present study investigated the contribution of slabs to the lateral load-carrying capacity of shear walls coupled with slabs. Cyclic lateral load tests were conducted on five two-story wall specimens at half scale. The test parameters included the thickness of the slab, the wall opening length, the use of punching shear reinforcement, and the use of parallel walls. The test results showed that, due to the slab effect, the strengths of the coupled wall specimens were 38 to 88% greater than the strength of the walls without the slab effect. Furthermore, the initial stiffness of the specimens was significantly increased by the slab effect. During early loading, local failure of the slabs occurred at the wall–slab connection. However, the coupled walls exhibited ductile behavior up to a 2% drift ratio, without significant degradation of strength. Nonlinear finite element analysis was performed on the test specimens. Based on the results, the initial stiffness and effective stiffness of the walls and coupling slabs were evaluated for the seismic design of coupled walls.

A three-dimensional (3-D) finite element method for prestressing and seating analysis has been developed. This method improves the accuracy of the results obtained using the widely adopted initial stress method and enables calculation of the seating loss effect, which is the final stress prediction of prestressing. Its application for large numbers of indeterminate-order structures is shown by comparing its calculation results with two-dimensional (2-D) conventional analysis, as well as with observed strain results for cables of an existing 462 m, six-span continuous bridge. With these considerations, a new management method of prestressing for jack force-diverting systems where the prestressing force does not focus uniquely on a design section was developed so that constructed prestressed concrete structures can be well-secured to comply with design objectives.