International Concrete Abstracts Portal

Concentrated shear deformation near the base of a squat wall, referred to herein as sliding shear, is one of the major mechanisms that can limit the strength and deformation capacity of reinforced concrete (RC) low-rise or squat walls. This paper reports tests of five large-scale RC squat wall specimens without axial load to investigate the effects of (1) longitudinal reinforcement layout, (2) shear stress demand, (3) high-strength materials, and (4) aspect ratio on the sliding shear behavior of squat walls. All specimens were tested under lateral displacement reversals. Test results indicate that the maximum strength of all test specimens with an aspect ratio of 0.5 was primarily associated with, or limited by, sliding shear at the wall base. For specimens with an aspect ratio of 0.5 and negligible axial load, the presence of special boundary elements did not have an apparent influence on wall behavior. Increasing the amount of longitudinal reinforcement, which also increased wall strength, resulted in less sliding deformation before 1.0% drift ratio. Beyond 1.0% drift ratio, all specimens with an aspect ratio of 0.5 exhibited a substantial pinching of the hysteretic response, where sliding along the wall base accounted for 80% of the overall deformation. Specimens with high-strength materials exhibited less deformation capacity than other specimens due to bar fracture at the wall base. As the aspect ratio increased to 1.0, the relative contribution of sliding deformation to overall drift decreased substantially to less than 20% of overall deformation. Based on the response characteristics of the test specimens, a sliding shear strength model for walls with negligible axial load is proposed. A database consisting of test results from fifty-five specimens (including five from this study) was developed to verify the proposed strength model.

The calculation of the nominal flexural strength of concrete members prestressed with hybrid (i.e., a combination of bonded and unbonded (steel and/or carbon fiber reinforced polymer (CFRP)) tendons is dependent on determining the stress in the unbonded prestressed reinforcement. Current provisions in the ACI CODE-318-25 are only applicable to members with either unbonded or bonded steel tendons. Additionally, while ACI PRC-440.4R-04 is adopted for unbonded CFRP tendons, neither ACI provisions address the use of hybrid tendons. This paper presents a closed-form analytical solution for the stress at ultimate derived based on the Modified Deformation-Based Approach (MDBA) that is applicable to beams prestressed with unbonded, hybrid (steel or FRP), external with deviators or internal tendons, with and without non-prestressed reinforcement. An assessment of its accuracy and applicability in calculating the nominal flexural strength is examined using a large database of 330 beams and slabs (prestressed with steel and/or CFRP tendons) compiled from test results by the authors as well as those available in the literature. Results predicted by the proposed approach exhibited excellent accuracy when compared to those predicted using ACI CODE-318 or ACI PRC-440 stress equations. They also show that the approach is universally applicable to any combination of bonded and/or unbonded (steel and/or CFRP) tendons, span-to-depth ratio, as well as loading applications.

Progressive collapse behavior of reinforced concrete frame buildings has been studied extensively, but most of the research has concentrated on frames containing seismic details. This paper presents results from analyses of the progressive collapse behavior of reinforced concrete frame buildings containing details used in regions of low seismicity following ACI CODE-318-19. The analytical simulations presented in this paper include the effect of moment redistribution that occurs after plastic moments are reached at sections of maximum moment. Ten-story 3-D frame models were designed in accordance with ACI CODE-318-19 and analyzed under progressive collapse scenarios involving the non-simultaneous removal of an interior and a corner perimeter column following ASCE 76-23. Nonlinear material behavior in these analytical models was captured using a lumped plasticity approach using hinge properties calibrated using results from laboratory experiments of full-scale sub-assemblages representing a portion of the perimeter frame containing details corresponding to non-seismic zones. The effect of catenary action in beams after column removal was included in the analyses, and the potential for premature shear failure of beams was assessed. Furthermore, models were also constructed to investigate the beneficial effects of increased rotational capacity of perimeter beams that result from using closer stirrup spacing at beam ends. This study demonstrates the importance of incorporating properly detailed continuous longitudinal bars enclosed within closely spaced closed stirrups at ends of beams of reinforced concrete frames in non-seismic zones to provide progressive collapse resistance. The study also highlights the importance of considering three-dimensional effects in models of frames to account for out-of-plane moment redistribution after loss of supporting elements.

Traditional analytical models have commonly been employed to assess the progressive collapse performance of building structures subjected to seismic loads. However, few studies addressed the effect of initial damage to adjacent components following the failure of a key component under explosion loads. In this paper, a damage assessment method for reinforced concrete structures was proposed based on the component analytical model, taking into account damage to adjacent members caused by close-in explosive scenarios. The reliability of the proposed analytical model was validated through comparison with experimental results in the existing literature. Besides, comparing the damage levels of a five-story reinforced concrete frame with those predicted by the proposed component models, the proposed assessment method based on components for predicting the damage degree of a reinforced concrete frame was validated to be reliable under a close-in explosion. The results indicated that the proposed analytical model can offer the advantage of not requiring a complex modelling process or the consideration of safety concerns associated with field explosion testing by comparing to numerical models of equivalent accuracy and experimental results.

A slag-based zero-cement concrete (ZC) was newly developed as an alternative, eco-friendly material to Portland cement concrete. To investigate the bond performance between ZC and steel reinforcing bars, lap splice tests were conducted for ZC beams. Fourteen beams (two cementitious normal concrete (NC) beams and twelve ZC beams) were tested at the ages of 6 days (45 MPa (6.53 ksi)) and 28 days (60 MPa (8.7 ksi)). For steel reinforcement, Grade 600 MPa (87.0 ksi) reinforcing bars were used. The test parameters included the concrete type, concrete strength (i.e., concrete age), reinforcing bar diameter, concrete cover thickness, ratio of actual lap splice length to required lap splice length, and use of stirrups. The test results showed that the performance of ZC beams was comparable to that of the counterpart NC beams in terms of moment–deflection relationship, damage mode, and reinforcing bar stress at the peak load. This result indicates that the bond performance of ZC was equivalent to that of NC with identical compressive strength. The bar development length specified in current design codes safely predicted the reinforcing bar stress of the ZC beams at failure: current design codes are applicable to the reinforcing bar development length design of ZC members.