International Concrete Abstracts Portal

Punching shear failure of RC flat slab connections cause loss of slab’s supports. The detached slab is falling and impacting the slab below. That problem requires thorough investigation and appropriate design guidelines. This paper presents research results on various aspects of this impact scenario. The analysis is based on an advanced numerical model that has been formulated, and the impact analyses follow the damage evolution in the concrete and reinforcement until complete connections failure of the impacted slab is developed, and a progressive collapse scenario starts. The effects of slab geometry and material properties were examined, and the contribution of special shear reinforcement and integrity rebars were investigated. The potential contribution of added drop panels to enhance slab resistance were examined. The slabs impact effect on the supporting columns has been investigated as well. The suitability of current static loading design-criteria to provide safe design against dynamic/impact punching shear is assessed. It shows that the current static-loading based design standards cannot ensure resilience of flat slab connections to impact loading and therefore cannot prevent a progressive collapse scenario. Analyses results are compared with inspected failure details of a collapsed RC flat slabs parking garage building, and excellent agreement is obtained.

This paper presents the prediction of bond strength between ultra-high performance concrete (UHPC) and fiber reinforced polymer (FRP) reinforcing bars using an artificial neuronal network (ANN) approach. A large amount of datasets, consisting of 183 test specimens, are collected from literature and an ANN model is trained and validated. The ANN model includes six variable inputs (bar diameter, concrete cover, embedment length, fiber content, concrete strength, and rebar strength) and one output parameter (bond strength). The model performs better than other models excerpted from existing design guidelines and previously published papers. Follow-up studies are expected to examine the individual effects of the predefined input parameters on the bond strength of UHPC interfaced with FRP rebars.

Reactive magnesia cement (RMC) is an emerging class of low-alkaline and CO₂-sequestering binder, which can mitigate the deterioration of GFRP reinforcements induced by a high alkaline environment, e.g., in Portland cement. This study investigated the slip behavior of GFRP rebar embedded in RMC composite, which varies with carbonation depth significantly. The variation of the interfacial bond was determined by a specially designed push-out test of the GFRP core; the variation of the carbonation degree and microstructure was examined by SEM-EDX, XRD, TGA, and acid digestion tests. Both properties demonstrated a similar trend, decreasing rapidly with increasing depth. A new finite element model that considers the depth-dependency of the matrix compositions and the rebar-to-matrix interfacial bond is established. It can predict the constitutive bond-slip behavior of a long GFRP rebar embedded in an RMC composite with non-uniform carbonation.

The American Concrete Institute (ACI) 440.1R-15 Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer (FRP) Bars linearly reduces the bar stress and thereby pull-out capacity of FRP bars to zero from an embedment length at 20 bar diameters (db) or less. Most experimental research and data examine the development length of various FRP bars at longer, more traditional, embedment lengths. A database was created from select available data in literature to compare to empirical standards. This investigation examines the bond performance of short embedded FRP bars into concrete considering a pull-out failure mode to expand the understanding of short embedded FRP bars into concrete. Based upon the database collected, for the glass fiber-reinforced polymer (GFRP) rebars, the current 440.1R appear quite conservative. For the basalt fiber-reinforced polymer (BFRP) rebar database collected, the current ACI 440.1R-15 provisions appear unconservative for a statistically significant number of the specimen test results within the database. In the case of the carbon fiber-reinforced polymer (CFRP) database, which is quite limited, the data appears to develop considerably less bond strength than the current 440.1R provisions might suggest which requires deeper investigation for the case of short embedment length bonded CFRP bars.

The serviceability and ultimate limit states of a concrete member are reliant upon the bond of reinforcement. The performance of glass fiber reinforced polymer (GFRP) reinforced concrete structures is influenced by multiple parameters and one of these parameters is the bond length of GFRP rebars. The scope of the present research is to experimentally study the effects of fully and partially bonded rebars on the load-bearing capacity and cracking of GFRP-reinforced concrete beams. The beams with partially bonded reinforcement show reduced capacities compared with those with fully bonded reinforcement, and the former reveals localized cracks. The partially bonded beams fail as a result of concrete splitting, while their fully bonded counterparts fail by concrete crushing.