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"Slabs"
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Transition between Shear and Punching in Reinforced Concrete Slabs: Review and Predictions with ACI Code Expressions
One-way slabs under concentrated loads may fail by one-way shear, two-way shear, flexure, or a combination of these modes. This paper reviews shear and punching shear-failure mechanisms of one-way slabs under concentrated loads tested from the literature and investigates the accuracy of different approaches to predict the ultimate capacity for such slabs using the ACI code expressions. A database with 160 test results was evaluated. Shear and concentrated loads measured at failure were reviewed according to parameters such as the load position, slab width, and reinforcement ratios. The load position and slab width play a marked influence on the failure mechanism and tested loads. The analyses improved the understanding of the main parameters influencing the behavior of one-way slabs under concentrated loads. Finally, the proposed effective shear width expression enables accurate shear capacity predictions using the ACI code expressions.
Journal Article
Alternative Punching Shear Design Methods for Concrete Slabs on Rectangular Columns
Worldwide punching shear design provisions for interior slabcolumn connections subjected to concentric shear differ greatly in how to account for column rectangularity (aspect ratio). In some, a reduced nominal shear capacity along the critical perimeter is assumed, whereas an effective or reduced critical perimeter is assumed in others. In this paper, three alternative methods to estimate the concentric punching shear capacity of interior rectangular slab-column connections without shear reinforcement, which implicitly account for the influence of column rectangularity and the ratio of the minimum column dimension to the effective slab depth, are presented. The accuracy of the proposed methods is studied through comparisons to 76 nonlinearfinite element models and 86 experiments. The predicted punching capacities from the proposed methods andACI 318-19 are also compared.
Journal Article
Subduction and Slab Detachment Under Moving Trenches During Ongoing India‐Asia Convergence
The dynamics of slab detachment and associated geological fingerprints have been inferred from various numerical and analog models. These invariably use a setup with slab‐pull‐driven convergence in which a slab detaches below a mantle‐stationary trench after the arrest of plate convergence due to arrival of continental lithosphere. In contrast, geological reconstructions show that post‐detachment plate convergence is common and that trenches and sutures are rarely mantle‐stationary during detachment. Here, we identify the more realistic kinematic context of slab detachment using the example of the India‐Asia convergent system. We first show that only the India and Himalayas slabs (from India's northern margin) and the Carlsberg slab (from the western margin) unequivocally detached from Indian lithosphere. Several other slabs below the Indian Ocean do not require a Neotethyan origin and may be of Mesotethys and Paleotethys origin. Additionally, the still‐connected slabs are being dragged together with the Indian plate forward (Hindu Kush) or sideways (Burma, Chaman) through the mantle. We show that Indian slab detachment occurred at moving trenches during ongoing plate convergence, providing more realistic geodynamic conditions for use in future numerical and analog experiments. We identify that the actively detaching Hindu Kush slab is a type‐example of this setting, whilst a 25–13 Ma phase of shallow detachment of the Himalayas slab, here reconstructed from plate kinematics and tomography, agrees well with independent, published geological estimates from the Himalayas orogen of slab detachment. The Sulaiman Ranges of Pakistan may hold the geological signatures of detachment of the laterally dragged Carlsberg slab.
Key Points
Kinematic context of slab detachment
Slab detachment during ongoing convergence
Journal Article
Effectiveness of Glass Fiber-Reinforced Polymer Stirrups as Shear Reinforcement in Glass Fiber-Reinforced Polymer- Reinforced Concrete Edge Slab-Column Connections
Recent years have seen a great interest in testing concrete slab-column connections reinforced with glass fiber-reinforced polymer bars (GFRP-RC). Yet, current fiber-reinforced polymer (FRP) codes and guidelines have not addressed the design of slab-column connections with FRP shear reinforcement. Results from an experimental investigation aimed at evaluating the effectiveness of glass fiber-reinforced polymer (GFRP) stirrups as shear reinforcement in edge slab-column connections reinforced with GFRP bars are presented. Four full-sized slabs with and without stirrups as shear reinforcement were tested to failure under combined vertical load and unbalanced moment. The effect of the GFRP stirrup type and extension on the punching shear response of the tested slab-column connections are analyzed and discussed. In addition, simplified design provisions to predicate the ultimate shear capacity of the tested specimens are proposed. The test results revealed that the presence of GFRP shear reinforcement as either closed or spiral stirrups within the slab around the column perimeter improved the punching-shear response of the tested connections. The results also indicated that the performance of the spiral stirrups was equivalent to or better than that of the closed stirrups in reducing the brittleness of the tested specimens with the same amounts of flexural and shear reinforcement. The proposed design provisions as extensions to those in CSA S806 design code yielded good, yet conservative predictions with an average [V.sub.tes]/[V.sub.pred] of 1.28 [+ or -] 0.24 for test specimens with FRP shear stirrups, as well as others with different types of FRP shear reinforcement found in the literature. This represents a step forward for engineers in designing two-way concrete slabs reinforced with FRP stirrups. Keywords: design codes; edge slab; flat slab; glass fiber-reinforced polymer; parking garages; punching shear; shear reinforcement; stirrups; unbalanced moment.
Journal Article
Seismotectonics beneath the Tokyo metropolitan area, Japan: Effect of slab-slab contact and overlap on seismicity
We first determine the configuration of the upper surface of the Pacific (PAC) slab beneath Kanto, Japan, from the distribution of interplate earthquakes relocated by an appropriate 1‐D velocity model. Then, traveltime tomography is carried out to estimate three‐dimensional seismic velocity structures around Kanto using 735,520 P wave and 444,049 S wave arrival times from 6508 local earthquakes. The obtained results suggest that the Philippine Sea (PHS) slab is subducting to depths of 130–140 km without a gap, even to the northwest of the Izu collision zone. We subsequently define the lateral extent of the contact zone between the bottom of the PHS slab and the upper surface of the PAC slab (PHS‐PAC interface) and reveal that the slab contact zone underlies a wider area beneath Kanto in harmony with the Kanto plain. The downdip limit of interplate (thrust‐type) earthquakes on the PAC slab is deepened by ∼30 km locally under the slab contact zone. This deepening is probably caused by a lower‐temperature environment in the PAC slab, resulting from the overlap with the PHS slab subducting above and consequent thermal shielding by the PHS slab from the hot mantle wedge. We detect an extremely low‐velocity anomaly in the easternmost portion of the PHS slab, which is probably attributable to serpentinization of mantle peridotite. Interplate earthquakes are almost absent along the PHS‐PAC interface overlain by the serpentinized mantle in the PHS slab, suggesting that ductile deformation takes place along the interface because of low viscosity of the serpentine.
Journal Article
The Effect of Voids on Flexural Capacity of Reinforced Concrete Slabs
The voided reinforced concrete slab system is mainly produced with polyester foam placed mostly at the bottom of the slab. The aim of the voids is to reduce the weight of the slab. In this paper behavior of the voided reinforced concrete slabs in which voids placed at the mid-height of the slab cross-section, is examined analytically. A series of models were created to come up with a lightweight slab. Two distinct slab models were analyzed using the ABAQUS software. In the first group, slabs had three layers, in which bottom and top layers were of solid reinforced concrete, but the mid layer was of voided unreinforced concrete. In the second layer, in order to increase the contact between top and bottom layers of the slab, crossties were utilized, and the mid layer was reinforced accordingly. Since all the layers were 5 cm thick, the total thickness of the slabs were 15 cm. Slabs were 100 cm wide and 200 cm long. They were simulated the three-point bending test. Concrete damaged plasticity material model (CDPM) for concrete and elastoplastic material model for steel was selected. From the results it was found that moment capacity decreased with the increase in the volume of the voids. There was a sudden decrease in strength after reaching the yield strength in voided slab without a crosstie. In addition, crossties enabled the reduction of the weight of the slabs without significant decrease in moment capacity.
Journal Article
Combined Beam-Slab Collapse Mechanism in Isolated Reinforced Concrete Beam-Slabs—Strength Design and Load Testing
In the conventional method of strength design of reinforced concrete (RC) beam-slab systems, it is assumed that if the beams are adequately stif, the slab and beams can be analyzed and designed separately under factored gravity loads. This paper demonstrates, through yield line analysis and load testing of isolated beam-slab systems, that such a design, which tacitly assumes a 'slab alone failure' mechanism, is irrational and overconservative (failing at a load level much higher than expected). The actual collapse of the conventionally designed beam-slab system invariably involves a combined beam-slab failure mechanism. It is therefore more rational and economical to design explicitly for such a collapse mechanism, accounting for plastic hinge formation in the beams along with yield lines in the slab. The proposed method suggests provision of minimum slab steel (as prescribed by the design code), and then designing the beams aiming for a combined two-way beam-slab failure. Experimental load testing establishes that the collapse occurs as planned and that the proposed economical design has the desired code-specified safety margins. Keywords: beam-slab system; combined beam-slab failure; rational design methodology; slab alone failure; yield line analysis.
Journal Article
Slab-on-Ground Analysis for Storage Rack Concentrated Uplift Loading
Slabs-on-ground supporting storage racks are often subjected to concentrated uplift under building code seismic forces. While methods for determining slab-on-ground capacity for downward loads are well-defined, guidance for resistance to uplift has been limited and relies on finite element analysis. A simplified approach is presented for calculating slab-on-ground uplift capacity as a function of slab thickness, reinforcement content, and storage rack frame depth. Testing is conducted on small-scale concrete samples in bending to obtain the material properties. Model slabs are created and tested for an upward and downward force couple representing concentrated seismic uplift on a reinforced slab-onground. The plastic hinge failure mechanism of the slab samples is correlated with finite element models, and straightforward formulas are developed to produce a table of uplift capacities for common storage rack and slab-on-ground configurations. Keywords: model concrete; seismic uplift; slab-on-ground (S.O.G.); storage racks.
Journal Article
Dynamic and probabilistic seismic performance assessment of precast prestressed reinforced concrete frames incorporating slab influence through three-dimensional spatial model
The dynamic and probabilistic seismic performances of precast prestressed reinforced concrete frames (RCFs) are assessed in this paper, and the slab influence in the overall structural behavior is considered during the process. The three-dimensional spatial model is established to provide the numerical basis, and the slab is modelled through L-/T-section beam-slab fiber-sections considering the effective width and centroid positions. The adopted model is verified with the experimental data, and the slab influence in hysteresis curves is investigated by parametric study. Then, two groups of precast prestressed RCFs are well designed to evaluate the slab influence in dynamic responses through seismic excitations, and the modal analysis, roof displacement analysis, maximum and residual drift ratio analysis are conducted for discussion. Moreover, the incremental dynamic analysis and fragility analysis are also conducted to investigate the probabilistic performance of precast prestressed RCFs with or without slabs. In general, different demand parameters [e.g., maximum interstory drift ratio (MIDR) and residual interstory drift ratio (RIDR)] may result in the variability of analyzing results, and ignoring the slab influence may underestimate the structural capacity under the frequent earthquakes and overestimate the structural capacity under the rare earthquakes. In a sense, the research proves the significance of slabs in the seismic performance of dry-connected precast prestressed RCFs, and meanwhile provides the reference for the further explorations of slab factors in precast concrete structures.
Journal Article