On June 24, 2021, a 40-year-old reinforced concrete flat plate structure building in Miami suffered a sudden partial collapse. This study analyzed the overall performance and key components of the ...collapsed building based on the building design codes (ACI-318 and GB 50010). Punching shear and post-punching performances of typical slab-column joints are also studied through the refined finite element analysis. The collapse process was simulated and visualized using a physics engine. By way of these analyses, weak design points of the collapsed building are highlighted. The differences between the reinforcement detailing of the collapsed building and the requirements of the current Chinese code are discussed, together with a comparison of the punching shear and post-punching performances. The simulated collapse procedure and debris distribution are compared with the actual collapse scenes.
•Punching behavior of GFRP reinforced single footings has been assessed.•Handmade shear bands have been used to enhance the punching strength of footings.•The use of handmade shear bands has led to ...an increase of the recorded peak loads.•Different codes showed far too conservative results than experiments.•CAN/CSA S806-12 yielded the most realistic results.
In the present study, four set of full scale specimens have been cast to investigate the effects of handmade GFRP shear bands on punching behavior of single footings. To do so, the specimens’ reinforcement was designed so that the punching failure governed. Besides, two types of concrete mixture, i.e. normal concrete (NC) and self-compacting lightweight concrete (SCLC) were used. Five Linear Variable Differential Transformer (LVDT) sensors have been installed on each specimen to record settlement as well as deflections. Moreover, the amounts of strain of bars and shear bands, caused by loading, at the edge of baseplate and two-way shear critical section have been recorded by installing strain gauges. The results show that the use of GFRP shear bands results in the increase of cracking resistance, maximum tolerable deflection, and recorded peak loads. In addition, it led to an increase of failure time which could warn occupants before complete failure.
•An extensive review for six decades of experimental punching shear testing of slabs under axial tension.•The effect of various parameter on punching shear behavior of slabs under axial tension.•A ...physically sound, simple, and accurate model for punching shear and axial tension is proposed.
Punching shear failure of reinforced concrete (RC) slabs is a sudden one, which has catastrophic outcomes. Flat slabs with large restrained dimensions, may be subjected to in-plane tensile forces due to thermal or earthquake loading. With the growing demand for optimum design and reduced safety factors, neglecting the effect of these forces on the punching shear design is not an option. Over the last 6 decades, research efforts have explained many issues regarding punching shear behavior of RC slabs subjected to in-plane compression loading. However, hand full of research investigations were directed towards studying those subjected to in-plane tensile forces. Even those limited studies were mostly experimental testing and comparison with design codes. The purpose of this study is to develop a physically sound mechanical model for concrete slabs under combined punching shear and in-plane tensile forces. Literature review for the experimental investigations, design codes and mechanical models for slabs under punching shear and in-plane tensile forces was conducted. A punching shear mechanical model, which explains the experimentally observed behavior of RC slabs under combined in-plane tensile forces and punching shear was developed and proposed. It captured the effect of various parameters in a physically sound manner as well as being consistent with the well-established critical shear crack theory.
Fiber reinforced polymer (FRP) serves as a prospective alternative to reinforcement in concrete slabs. However, similarly to traditional reinforced concrete slabs, FRP reinforced concrete slabs are ...susceptible to punching shear failure. Accounts of the insufficient consideration of impact factors, existing empirical models and design provisions for punching strength of FRP reinforced concrete slabs have some problems such as high bias and variance. This study established machine learning-based models to accurately predict the punching shear strength of FRP reinforced concrete slabs. A database of 121 groups of experimental results of FRP reinforced concrete slabs are collected from a literature review. Several machine learning algorithms, such as artificial neural network, support vector machine, decision tree, and adaptive boosting, are selected to build models and compare the performance between them. To demonstrate the predicted accuracy of machine learning, this paper also introduces 6 empirical models and design codes for comparative analysis. The comparative results demonstrate that adaptive boosting has the highest predicted precision, in which the root mean squared error, mean absolute error and coefficient of determination of which are 29.83, 23.00 and 0.99, respectively. GB 50010-2010 (2015) has the best predicted performance among these empirical models and design codes, and ACI 318-19 has the similar result. In addition, among these empirical models, the model proposed by El-Ghandour et al. (1999) has the highest predicted accuracy. According to the results obtained above, SHapley Additive exPlanation (SHAP) is adopted to illustrate the predicted process of AdaBoost. SHAP not only provides global and individual interpretations, but also carries out feature dependency analysis for each input variable. The interpretation results of the model reflect the importance and contribution of the factors that influence the punching shear strength in the machine learning model.
A variable magnetic permeability is introduced to the skin effect coefficient to reflect the influence of flux density variation on eddy current losses. The evaluation results show that the new iron ...loss model can cover a wide range of frequencies without using piecewise functions. Two types of punched edges are defined and the additional iron losses are tested, separated, and modeled, so that the punching and burrs' connection effects on iron losses can be considered more accurately. The iron loss model proposed in this article is very useful for a more accurate design of high-speed motors including the punching effects.
An approach is provided to modify model uncertainty related to punching shear resistance of fat slabs. Model uncertainty of six shear strength models in different design codes are investigated ...systematically. Based on 452 punching tests of concentrically loaded slabs, the computational accuracy of six punching shear strength models is compared. Characteristic values of model uncertainty with different specific assurance rates are determined based on the probabilistic characteristics of computational model uncertainties. The comparison shows that the accuracy of the draft of the next generation of the Eurocode 2 model is superior to the Chinese, American, and Canadian code models, which usually underestimate the punching shear resistance of fat slabs. Furthermore, the model uncertainty of the Chinese, American, and Canadian code models follow a normal distribution, whereas the model uncertainty of the other three models obey lognormal distribution. Keywords: design code; model uncertainty; punching shear strength model; reinforced concrete slab-column connections; statistical characteristics.
•The behaviour of UHPC/NC hybrid slab is investigated.•A validated FE model is used to study a wide range of parameters.•A design model is developed to predict the punching capacity of hybrid slabs.
...Flat slabs are commonly used in the construction of multi-storey buildings due to their ease of placement and installation, relatively short construction time, minimal structural floor depth and economic credentials. However, flat slabs are vulnerable to punching shear, a failure mode that typically occurs without any warning at slab-column connections. While various methods exist to improve punching shear capacity, the use of ultra-high performance concrete (UHPC) offers a highly buildable alternative to use of shear reinforcement in normal strength concrete (NC). However, UHPC is an expensive material and recent research has focussed on its partial use in column zones only, with NC elsewhere i.e. hybrid NC/UHPC. In this paper, a non-linear finite element (FE) model using ABAQUS was developed to simulate the punching shear performance of hybrid NC/UHPC flat slabs without shear reinforcement. The FE model was validated against experimental results from the literature. The validated model was then used to investigate the influence of slab thickness, column size, UHPC area and UHPC compressive strength. The results show that punching shear capacity of the slabs increases with the area of the UHPC zone. Additionally, the ratio of concrete compressive strength of UHPC to that of NC has a significant effect on the behaviour of the hybrid slabs which should be accounted for in future design guides. In order to understand the performance of existing design guides and codes in this context, a comparison between FE results and code predictions is also presented. The results suggest that the code models including ACI 318-14, Eurocode2 and Model Code 2010 cannot accurately estimate the punching shear capacity of reinforced UHPC slabs and hybrid NC/UHPC slabs. A modification to the existing ACI equation is proposed which yields accurate predictions for reinforced UHPC and hybrid slabs.
•Punching shear failure was observed in both tests.•The majority of the applied loads transferred to the columns nearest to the removed one(s).•The post-failure stages largely enabled the slab to ...resist collapse.•Two column removal reduced load capacity but increased the deformation cpacity.
Existing studies on progressive collapse of reinforced concrete (RC) flat plate structures have mainly focused on single column loss scenarios. However, accidental events, such as earthquakes, blasts or vehicle collisions, may cause a more severe initial damage beyond the loss of only one column. To fill this gap in knowledge, this study reports two quasi-static large-displacement experimental tests on two nominally identical 1/3-scale, 2 × 2-bay RC flat plate substructures under an edge-column (S-E) and an edge-interior-column (S-EI) removal scenarios. Two types of uniformly distributed loads (UDLs) were applied to the slab in the two tests: (1) an increased UDL during the tests on the bays adjacent to the removed column(s) and (2) a constant 5 kPa UDL elsewhere to simulate the design live load. In both tests, punching shear failures were observed and led to the first peak loads (FPLs) which were all followed by a sharp load drop. Subsequently, the load increased again to reach the post-failure peak loads (PPLs). The experimental results showed that the PPL was 9.6% higher than the FPL in S-E and 81.9% higher in S-EI. Relative to S-E at the PPL, S-EI presented a more ductile structural behaviour, in which the applied load at the PPL was 26.9% lower, but with a 112% larger displacement, than S-E. In both tests, tensile membrane actions were observed at large deformations and found to be essential in developing post-failure capacities. Such resisting mechanism cannot be neglected when investigating progressive collapse of RC flat plate structures. The yield line theory was found to overestimate the flexural capacity of the two tests.
A punching test for simply estimating the tensile strength and total elongation of steel sheets and formed parts was proposed. The tensile strength and total elongation were estimated from the shear ...stress at the maximum punching load and percentage of the burnished depth at the sheared edge of the slug measured without cutting, respectively. For a variety of steel sheets with a range of the tensile strength from 360 to 1500 MPa, linear functions for the estimation were experimentally obtained. The correlation of the estimated tensile strength of the steel sheets with the measured one from the uniaxial tensile test was considerably high, and the correlation of the estimated total elongation was high. The distributions of tensile strength and total elongation for hot- and cold-stamped parts were estimated. The proposed punching test is available under not only a laboratory environment but also a factory environment.
In this paper, an effective ultrasonic-assisted micro-punching method for thin stainless sheet metal with molten plastic as flexible punch is adopted. The minimum micro hole and arrays with diameter ...of 0.3 mm were punched on rolled state thin stainless sheet metal with a thickness of 10 μm. The deformation mechanism and forming parameter quality were investigated. The experimental results show that cylinder pressure, ultrasonic power, and ultrasonic vibration time were the key parameters which affect each other. The ultrasonic vibration time needed to be properly set up according to the preset cylinder pressure and ultrasonic power to form a complete punching hole and avoid defects or cracks of the parts. For the micro hole with a diameter of 0.6 mm punched on a thin stainless sheet metal with a thickness of 30 μm, there are no significant effects on the qualities of the punching fracture surfaces when changing the punching parameters in the range of the cylinder pressure of 0.3–0.5 MPa and the ultrasonic power of 60–90%. In the case of cylinder pressure 0.5 MPa and ultrasonic power 75%, the width of shearing zone is between 10 and 29%, and the surface roughness Ra of the shearing zone is in the range of 0.10–0.20 μm. Our results could throw light on improving the fracture surface quality of micro-punched part obtained by ultrasonic micro punching with flexible punch.
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