International Concrete Abstracts Portal

To secure emulative seismic performances of precast concrete (PC) special moment frame buildings, two capacity-based connection design options (that is, strong and ductile precast connections) are provided in the current version of ACI 318. However, the evolving performance-based seismic design and response evaluation requires a reasonable estimation of the energy dissipation and corresponding hysteresis damping characteristics so that their potential performance level can be properly predicted. Therefore, this study focuses on the seismic performances, especially the energy dissipation and damping performances of the Code- compliant PC wide beam-column connections. Three PC wide beam-column connection specimens under the ductile connection design principle with different joint details and a reinforced concrete (RC) control specimen were fabricated and tested under reversed cyclic loadings. In addition, an energy-based macro-modeling method was developed to characterize the cyclic responses, including the damping response of PC wide beam-column connections. The test results revealed that the Code-required overstrength of shear-friction strength between PC beam members and cast-in-place (CIP) concrete is crucial to achieving the ductile performance of precast connections. It also appeared that the energy-based macro-modeling method could capture the hysteresis features through the relationship between the equivalent viscous damping (EVD) ratio and the ductility capacity of PC wide beam-column connections.

The geometry of arched (vertically curved) reinforced concrete (RC) members contributes to the development of additional stresses, affecting their flexural and shear strength. This aspect of curvilinear RC members reinforced with GFRP bars has not been reported in the literature. In addition, there are no specific design recommendations that consider the effect of curvilinearity on the flexural and shear strength of curved GFRP-RC members. This study has performed pioneering work in developing models to predict the flexural and shear strength of curvilinear GFRP-RC members with a focus on precast concrete tunnel lining segments. Eleven full-scale curvilinear GFRP-reinforced tunnel segment specimens were tested under bending load as the experimental database. Then, a model was developed for predicting the flexural strength of curvilinear GFRP-RC members. This was followed by the development of two shear-strength prediction models based on the modified compression field theory (MCFT) and critical shear crack theory (CSCT). After comparing the experimental and analytical results, a parametric study was performed to evaluate the effect of different parameters on the flexural and shear strength of curvilinear GFRP-reinforced members. The results indicate that neglecting the curvilinearity effect led to a 17% overestimation of the flexural capacity, while the proposed models could predict the flexural capacity of the specimens accurately. The proposed models based on the MCFT—referred to as the semi-simplified modified compression field theory (SSMFT) and the improved simplified modified compression field theory (ISMCFT)—predicted the shear capacity of the specimens with 28% conservatively. In addition, the modified critical shear crack theory (MCSCT) model was 10% conservative in predicting the shear capacity of curvilinear GFRP-RC members.

An experimental investigation was conducted to evaluate the shear-friction capacity of cylindrical pocket connections without reinforcement crossing the interface, which is a common connection detail between precast concrete substructure elements. Current Code expressions for shear-friction capacity include components for cohesion or aggregate interlock and contribution from steel crossing the interface or a clamping force. These expressions were primarily derived and calibrated based on pushoff tests with reinforcement crossing the shear plane, which do not represent the behavior of the shear plane in a cylindrical pocket connection. Thirty-four large-scale specimens were built and tested to investigate the shear friction of the cylindrical pocket connection without reinforcing steel crossing the shear plane. This experimental study showed that current Code expressions provided conservative estimates for this connection. A revised proposed theory is presented that more accurately predicts the shear-friction capacity of this connection without interface steel.

To reduce CO2 emissions of concrete, a slag-based zero-cement concrete (ZC) of high strength (60 MPa [8.70 ksi]) was developed. In the present study, cyclic loading tests were conducted to investigate the seismic performance of full-scale interior precast beamcolumn joints using the new ZC. One monolithic portland cementbased normal concrete (NC) beam-column joint and two precast ZC beam-column joints were tested. The test parameters included concrete type, fabrication method, and beam bottom bar anchorage detail. The structural performance was evaluated, including the strength, deformation capacity, damage mode, and energy dissipation. The test results showed that the structural performance of the precast ZC beam-column joints could be equivalent, or superior, to that of the monolithic NC beam-column joint. Although the reinforcement details of the ZC joints do not satisfy the seismic design requirements of special moment frames in ACI 318-19, the seismic performance of the ZC joints satisfied the requirements of ACI 374.1-05 and AIJ 2002 Guidelines.

In this study, full-scale loading tests were conducted to investigate web-shear strengths of hollow-core slab (HCS) members strengthened in shear by using practically viable methods. All the HCS units used in the current test program were fabricated by using the individual mold method, not by the extrusion method, and the key experimental variables of the shear test were set as the presence of shear reinforcement, core-filling concrete, topping concrete, and also the magnitude of effective prestress. The shear force-displacement behaviors, crack patterns, and strain response of shear reinforcements were reported in detail. In addition, to identify the shear strength enhancement provided under various strengthening conditions in a quantitative manner, existing shear test results of series specimens, including a naked HCS member and corresponding composite HCS members with cast-in-place (CIP) concrete and/or shear reinforcements, were collected from literature. On this basis, a practical design expression capable of estimating shear strengths of HCSs strengthened with CIP concrete and stirrups was suggested based on the ACI 318 code equation. The proposed method evaluated the shear strengths of the collected specimens with a good level of accuracy, regardless of the presence of corefilling concrete, topping concrete, and shear reinforcements.