The evolution of the seismic design provisions in response to the lessons learned from previous earthquake events has led to the development of new design methodologies such as performance-based design (PBD). A key component of PBD is to lay out the engineering demand parameters identifying the initiation of different damage states (e.g., yielding, spalling, bar fracture, etc.). In this regard, reliable knowledge of structural members’ strength and deformation capacities is required, and it is often obtained through quasi-static cyclic testing programs. The selecting of an appropriate loading protocol is crucial in these programs to achieve.
(1) New approaches for the selection of ground motion for experimental tests;
(2) Performance of reinforced concrete structural walls tested under different types of quasi-static cyclic and dynamic loading;
(3) Imposed loading protocols versus damage states and performance criteria for RC structural walls considering uni- and bi-directional loading;
(4) Performance of concrete truss girder connection reinforced with steel or FRP double-headed bars tested under quasi-static cyclic loading.
This session has been AIA/ICC approved for 2 CEU/PDH credits.
Dynamic Response of SMA-UHPFRC Reinforced Bridge Piers under Lateral Impact Loading
Presented By: AHM Muntasir Billah
Affiliation: University of Calgary
Description: Reinforced concrete (RC) bridge piers are potentially at risk of failure when they are subjected to accidental lateral impact loads such as vehicle collision. Although the combined effect of ultra-high-performance fiber-reinforced concrete (UHPFRC) jacket and shape memory alloy (SMA) rebars have been widely investigated on behaviors of bridge piers when exposed to seismic loads, there exists no research work that has attempted to investigate the response of bridge columns constructed with SMA rebar and UHPFRC when subjected to lateral impact loads. This study numerically evaluates the dynamic behavior and damage states of an RC bridge pier strengthened with UHPFRC jacket and reinforced with SMA rebars under lateral impact loads considering the variations of different parameters including the type of SMA rebars, the thickness of UHPFRC jacket (tU), impact velocity (Vimp), and axial load ratio (ALR). In this study, exploring optimal levels for the thickness of UHPFRC jacket and the length of SMA rebars is of interests.
Structural Wall Deformation Limit States and Impact of Loading Protocol
Presented By: Saman Abdullah
Affiliation: University of Sulaimani, Kurdistan, Iraq
Description: A framework for defining component deformation limits for inspection and repair triggers for reinforced concrete structural walls is developed, which are used in post-earthquake assessment procedures to identify locations for visual inspection and identify locations needing structural repair. As part of the study, experimental test data are reviewed to understand the impact of loading protocol on residual capacity of concrete walls. The study focuses on defining the deformation limit beyond which: (a) the number of loading cycles starts influencing the cyclic behavior (strength and deformation capacity) of concrete walls and (b) the prior loading history starts influencing the residual (reserve) capacity (in terms of strength and deformation capacity) of the wall for subsequent loading events. This component deformation limit was found to correspond to the deformation at the initiation of lateral strength loss (LSL), which coincides with initiation of buckling of boundary element longitudinal bars for flexure-controlled, code-compliant, walls.
Performance Evaluation of Low-Rise RC Walls Using Dynamic and Quasi-Static Loading Protocols
Presented By: Julian Carrillo
Affiliation: Universidad Militar Nueva Granada, Colombia
Description: Quasi-static (QS) tests are the simplest method to be carried out; however, they are unsuited for providing information on the dynamic behavior of specimens subjected to earthquake-induced deformations. Experimental evidence supporting the fact that results from QS test of low-rise reinforced concrete walls may be safely assumed as a lower limit of strength and displacement, and energy dissipation capacities are still scarce. This work compares the performance of 12 isolated full-scale reinforced concrete (RC) walls for low-rise housing: six prototype walls tested under Quasi-static cyclic (QSC) loading and six models tested under shaking table excitation. Variables studied were wall geometry (solid walls and walls with openings), type of concrete (normal weight and lightweight), web steel ratio (0.125% and 0.25%), type of web reinforcement (deformed bars or welded wire meshes), and testing method (shaking table and QSC testing). Comparison of the results from dynamic and QSC tests indicated that stiffness and strength properties were dependent on the loading rate, the strength mechanisms associated with the failure mode, the low-cycle fatigue, and the cumulative parameters, such as displacement demand and energy dissipated. It was verified that loading history of the QSC testing ignores the foremost dynamic effects observed in structures subjected to earthquake loads. Then, data obtained from QSC tests cannot always be safely assumed as a lower conservative limit of the performance capacity of RC walls for low-rise housing subjected to earthquake-induced deformations.
Comparing Uni- and Bi-Directional Tests on RC Walls
Presented By: Katrin Beyer
Affiliation: EPF Lausanne
Description: Most reinforced concrete (RC) wall tests simulate earthquake effects as uni-directional loading. Less than 1% of all quasi-static cyclic tests on RC walls have been conducted as bi-directional tests, in which walls are subjected to loading along both horizontal axes. Bi-directional tests require larger and more complex test setups than uni-directional tests and therefore should only be pursued if they provide insights and results that cannot be obtained from uni-directional tests. This presentation reviews various bi-directional loading protocols and summarizes trends with regard to stiffness, strength and deformation capacity of walls under bi-directional loading when compared to uni-directional loading. In addition, the effect of the loading history on the torsional stiffness of RC core walls is revisited. The presentation concludes with an outlook on future research needs. The presented work was initiated through a working group of the NSF SAVI Wall Institute led by Prof. John Wallace.
Loading Protocols for RC Prism Axial Tests to Assess Seismic Performance of Ductile Walls
Presented By: Rajesh Dhakal
Affiliation: University of Canterbury NZ
Description: Seismic performance of flexurally dominated ductile reinforced concrete (RC) structural walls is primarily governed by the behavior of its end confined regions known as boundary zones. In lieu of resource intensive experimental tests on wall specimens, several research groups have adopted a simplified approach of conducting uniaxial cyclic tests on RC prisms representing wall boundary zones to investigate the failure modes (e.g., bar buckling, out-of-plane instability, etc.) that are likely to initiate in these regions. With change in the testing regime from a complete wall unit to an idealized wall boundary prism, laboratory testing also warrants a change in the cyclic loading pattern from lateral displacements to representative axial displacements. Conventional quasi-static uniaxial cyclic loading protocols comprising of repeated cycles at progressively increasing axial displacement amplitudes are often employed without due consideration towards the excessive cumulative damage caused by the multiple moderate and large amplitude cycles. However, earthquakes typically induce a random cyclic loading sequence dominated by small amplitude cycles with only a few large amplitude cycles, which makes the test results obtained using the conventional loading pattern unrepresentative of the boundary zones’ response during earthquakes. In this study, quasi-static uniaxial cyclic loading protocols that are representative of the average inelastic axial deformation demands anticipated in the wall boundary zones under earthquakes are developed following a simplified numerical procedure. The proposed loading protocols are defined in terms of the inelastic axial strain demands on the boundary zones corresponding to the prescribed performance-based lateral drift limits of the structural walls.
Cyclic Performance of Concrete Truss Girder Connection Reinforced with Steel or FRP Double-Headed Bars
Presented By: Mamdouh El-Badry
Affiliation: University of Calgary
Description: Corrosion of steel reinforcement within concrete is a leading cause of deterioration of concrete bridge components. A novel corrosion-resistant hybrid system has been developed to eliminate corrosion-related problems in short- and medium-span concrete bridges . The system is composed of transversely spaced precast prestressed truss girders and a cast-in-place or precast concrete deck slab acting compositely with the girders. Each truss girder consists of top and bottom concrete chords connected by vertical and diagonal truss members made of concrete-filled FRP tubes (CFFTs). Long double-headed bars (LDHBs) made of steel or fiber-reinforced polymer (FRP) protrude from the CFFTs to connect the vertical and diagonal truss members to the chords . As part of an ongoing comprehensive research program, this paper presents the results of cyclic load testing of specimens built up of a segment of the truss girder in consisting of one vertical and one diagonal member connected to a portion of the top and bottom chords. Four full-scale specimens were fabricated and tested. In two of the specimens, steel double-headed bars (SDHB) were used to reinforce and connect the CFFT members to the top and bottom portions of the chords. In the other two specimens, glass FRP double-headed bars (FDHB) were used. During testing, the bottom chord portion was anchored to the laboratory's strong floor while a horizontal load was applied to the top chord portion. One SDHB-reinforced specimen and one FDHB-specimen were tested under monotonic loading increasing from zero to failure. The other two specimens were tested under quasi-static cyclic loading with increasing amplitude in accordance with the loading protocol and recommendations of ACI 374.2R-13. Large amount of recorded data and collected damage images, the most important of which were the horizontal load and the top chord and CFFT member deformations as well as the strains in the LDHBs.