Summary

Motivation & Scope:

Significantly lighter members for structural walls in moderate seismic zones are a viable possibility by using high-strength concrete and incorporating ductile shear failures as a new genre of ductile failure mechanisms. Recent research on the seismic design of hollow piers has provided new insights on the accurate assessment of elastic and inelastic web-crushing shear capacity of structural walls with boundary elements. Ductile shear failures, displayed as web-crushing failures or yielding of the transverse reinforcement at relatively high levels of displacement ductility, allow for easy repair since damage to the boundary elements can be minimal. The advent of high-strength concrete has generated great interest in the promise that it may provide for cost-effective seismic design. However, its potential cannot be fully realized due to current outdated and prescriptive design criteria. Rational assessment models show that web-crushing is linearly related to concrete compressive strength, indicative of new possibilities for increased shear capacities of lighter members with increased concrete strength. This project will verify this promise by establishing the inelastic web-crushing limits for structural walls.

Approach:

The research objectives are pursued through integrated experimental and analytical investigations. The first part of the experimental investigation will focus on the determination of dependable limits to web-crushing failures for ductile shear response in HSC structural walls through 8 quasi-static monotonic and cyclic tests on 1/4-scale walls with concrete strengths of 34, 69, 103, and 137 MPa. These tests will be conducted at MSU’s Civil Infrastructure Laboratory. Parallel analytical investigations are focusing on the development and validation of assessment tools for structural walls loaded in their principal and diagonal directions through 3D non-linear finite element models and simpler sectional analyses. Using the improved assessment models, two 1/4-scale HSC (137 MPa) wall assemblies analogous to hollow piers will be designed and tested under bi-directional loading. These system tests will be conducted at the Multi-Axial Subassemblage Testing (MAST) NEES facility at the University of Minnesota-Twin Cities. One assembly will be designed to obtain a web-crushing failure at low ductility levels to validate the established limits for systems under combined loading. The second unit will be designed to fail in a ductile shear failure mode at high ductility levels. Conventional and advanced non-contact strain measurements will be correlated with analysis results to fundamentally understand the associated deformation limits. Rational, yet simple, assessment models will be developed to provide designers with practical tools for the design of HSC structural walls with reliable ductile shear failure modes.