Quasi-static Loading Regime Research Articles

Real collapse responses of an RC flat plate structure under extreme overloading condition: Reversing load redistribution

Progressive collapse research of concrete flat plate structures, typically investigated through the alternate path (AP) method with a focus on column failure (removal), has often neglected the facts of real-life collapse events which are caused by slab overloading, leading to initial punching shear failure at slab-column joints. Progressive collapse of the structural systems triggered by slab-column joint failures exhibits distinct failure modes and resistance mechanisms from those triggered by column failures. Building upon our initial tests on the overloaded slab specimen under quasi-static loading regimes, this paper presents an innovative experimental study that closely mirrors the load-resistant mechanisms of the most common collapse incidents in flat plate structure systems in the real world. By successively stacking up gravity loads without additional interventions, the test accurately simulates the spontaneous failure conditions typical of flat plate structures. A key discovery of this research is the identification of a unique reversing load redistribution mechanism, a phenomenon not previously observed in our slab overloading tests or in studies focused on column removal scenarios. This discovery highlights the necessity of enhancing the post-punching capacity at the slab-column joints as a critical factor in preventing collapses due to slab overloading. In addition, this study provides an in-depth examination of the dynamic effects inherent in the progressive collapse of flat plate structures. Evaluating the dynamic increase factor and load amplification factor offers supplementary data pertinent to real-world collapses, providing essential insights for improving the resilience of flat plate structures against initial joint failure due to slab overloading.

Elasticity of dense anisotropic carbons: A machine learning model of the structure–property relationship informed by large scale molecular dynamics data

Dense anisotropic carbons are praised materials for thermostructural applications, yet, so far, a detailed structure–property relationship for these materials is still lacking, especially for the pyrocarbon (pyC) matrices in carbon/carbon composites. Here we compute the full elastic tensors of 210 recently introduced nanoscale models of anisotropic carbons (Polewczyk et al., 2023), covering domain sizes (Lc and La) and orientation angles (OA, as a measure of nanotexture) relevant to most as-prepared and moderately heat-treated pyC matrices: Lc∈ [1.5:8 nm]; La∈ [2:5.5 nm]; and OA ∈ [25:110°]. Isothermal and adiabatic elastic tensors, corresponding to the slow quasi-static and ultra-fast loading regimes, respectively, are considered. Analyzing the database of computed elastic constants with a random forest regressor supervised learning algorithm we show that all elastic constants can be predicted accurately using Lc, La and OA as descriptors. Among the latter, OA is the one showing, by far, the strongest correlation with the elastic tensors. For such dense, non porous carbons, 3 of the 6 isothermal and 5 of the 6 adiabatic constants can even be accurately predicted using OA as the unique material descriptor. Calculation of the universal anisotropy index shows that isothermal tensors show more anisotropy than adiabatic ones, indicating that stress relaxation favors elastic anisotropy. Eventually, the Young’s moduli and Poisson coefficients of six models of actual pyCs are presented and their longitudinal moduli compared to tensile measurements, showing relatively poor agreement. These results suggest that accounting for texture at a larger scale is required to capture pyC matrices elasticity. The developed supervised learning model is available for online use at https://web.ism.u-bordeaux.fr/rfr.

Effect of infill walls on progressive collapse behavior of self-centering precast concrete frame

To study the effect of infill walls on the progressive collapse resisting-performance of self-centering precast concrete (PC) frame structures, three 1/2 scaled, two-span and two-story self-centering PC frame specimens with and without infill walls were tested under quasi-static pushdown loading regime. The test results showed that the failure modes of self-centering PC frames were governed by concrete cracking and local spalling at the beam ends under progressive collapse scenario. Compared with self-centering bare frame, the presence of infill walls provided additional load path, thereby reducing the concrete damage at the beam ends to some extent. The full infill walls with lower strength could still increase the initial stiffness and peak resistance of self-centering bare frame to 2.47 times and 1.33 times, while the infill walls with 20% opening ratio could increase to 2.21 times and 1.19 times, respectively. Nevertheless, the infill walls also reduced the self-centering capacity of the structures. Numerical analyses further indicated that the magnitude of prestress force of steel strands between beams and columns, the strength of bed joints as well as the width of infill walls had a great effect on the progressive collapse of self-centering infilled frames. Finally, based on numerical results, a reduction factor formula was proposed to quickly estimate the structural resistance of self-centering infilled frames with different opening ratios.

Experimental study on progressive collapse of self-centering precast concrete frame with infill walls

The self-centering precast concrete (PC) frame has been proved to perform excellently under seismic load in many studies. However, its progressive collapse-resisting mechanism, especially in the presence of infill walls need to be investigated further. Three 1/2 scaled self-centering PC frame specimens, including one self-centering PC frame and two self-centering infilled PC frames were tested under quasi-static pushdown loading regime. The test results showed that the damage of self-centering bare frame was mainly concentrated at the beam ends under vertical load. The compressive arch action (CAA) and the tensile force in the prestressed strands undertook the vertical load together at the beginning of the test. The infill walls with lower strength could still obviously enhance the initial stiffness and progressive collapse resistance of self-centering frame, but did not change the failure location of the frame. The initial stiffness of self-centering infilled frame was 2.47 times of self-centering bare frame, and the peak load in the CAA stage was 1.33 times. The additional load path produced by the infill walls mitigated the concrete damage at the beam ends, thereby improving the ductility performance and repairability of the beams. As the beam span of self-centering infilled frame decreased by 1/4, the initial stiffness and peak load in the CAA stage increased by 1.65 times and 1.66 times respectively. Nevertheless, the concrete damage at the beam ends became severer and the ductility of the frame was reduced.

Experimental and numerical investigation on progressive collapse of self-centering precast concrete frame with infill walls

Two 1/2 scaled self-centering precast concrete (PC) frames with and without infill walls were experimentally and numerically investigated under quasi-static pushdown loading regime. The test results showed that the main failure modes of self-centering PC frames were concrete cracking and spalling at the beam ends. Compared with self-centering bare frame, since the infill walls undertook partial vertical loads, the concrete damage at the beam ends of self-centering infilled frame was reduced. Since the lower strength of AAC blocks and mortar, the presence of infill walls did not change the failure mode and failure location of self-centering PC frame. The infill walls with lower strength could still significantly enhance the initial stiffness and collapse resistance of the structure. However, infill walls also reduced the self-centering capacity of the structure. The simulation results indicated that the prestress force of steel strands between beams and columns had a greater effect on the structural resistance of self-centering PC frames. For the self-centering infilled frames, the progressive collapse-resisting capacity of infill walls mainly depended on the strength of bed joints, while the effect of the cross joints was negligible. When the mortar joints had a lower strength, the increase in block strength had limited effect on the increase in structural resistance. With the increase of strength of mortar joints, the effect of variation of block strength on the structural resistance became obvious. Finally, the proposed analytical method had a relatively better accuracy to predict the vertical resistance of self-centering PC frames.

Influence of specimen profile size and thickness on the dynamic compressive behavior of rigid PVC foams

Split Hopkinson Pressure Bar (SHPB) apparatuses were extensively utilized in the dynamic testing of polymeric foams in previous studies; however, there are many technical limitations on the specimen size when utilizing SHPBs. Consequently, most research on the influence of specimen size on the mechanical response was limited to the quasi-static loading regime. The specimen size effect was reported to be negligible in the quasi-static regime. This observation was traditionally extrapolated to the dynamic regime; however, the hypothesis has not been thoroughly verified by experimental testing. The present study represents the most thorough investigation (to date) on the influence of specimen shape, cross-sectional area and thickness on the dynamic mechanical response of Polyvinyl Chloride (PVC) foams. A drop tower testing machine equipped with a massive 45.45 kg dropping entity and a novel sacrificial energy dissipation system was employed for the dynamic testing. The findings from this work revealed a significant sensitivity to the specimen profile on the dynamic mechanical response of PVC foams in contrast to the negligible effects in the quasi-static regime. Investigating the effect of specimen thickness on the mechanical response further demonstrated that the engineering strain rate is not a suitable index for reporting PVC foams’ rate sensitivity. Instead, the impact velocity is more appropriate since specimens with different thicknesses exhibited a similar compressive stress/strain response when tested at the same impact velocities while experiencing different engineering strain rates. The influence of specimen shape (rectangular versus cylindrical) was negligible in both the quasi-static and dynamic regimes.

Investigation of the Mechanical Behaviour of Lingulid Sandstone Emphasising the Influence from Pre-Existing Structural Defects, Part 1: Model Identification Based on Static Experiments

A constitutive model able to describe both tensile damage and plastic deformation under confinement is a prerequisite to numerically simulate the behaviour of sandstone rock under an impact loading induced in a percussive drilling process. Therefore, model identification under both tensile and high confinement states is needed. In the present work, an experimental investigation was carried out in order to determine the mechanical properties of a sandstone rock for the purpose of advanced constitutive model identification. Different testing methods were used in quasistatic and dynamic loading regimes. This first part of the study is dedicated to static experiments, whereby three-point bend tests were first performed to evaluate the quasistatic tensile strength of the rock and its distribution by employing the Weibull statistics. Secondly, direct compression tests were conducted to evaluate the stiffness and strength in an unconfined condition. Afterwards, quasioedometric compression (QOC) tests were carried out in order to obtain the deviatoric and volumetric behaviours of the material as a function of the hydrostatic pressure (up to 375 MPa). In these QOC tests, the metallic confinement cell was instrumented with strain gauges to deduce the state of the stress and strain within the sample. A linear volumetric response along with a continuous increase of strength with the level of hydrostatic pressure was observed. This experimental work points out that, under unconfined loading (three-point bending and uniaxial compression), pre-existing structural defects play a major role leading to a highly scattered behaviour in terms of sample stiffness and ultimate applied load. On the other hand, under high confinement levels (QOC tests), beyond the nonlinear response of the curve foot, the influence from structural defects was observed to be small.

Load-rate effects on the in-plane compressive behaviour of additively manufactured steel 316L honeycomb structures

Additive manufacturing (AM) offers the opportunity to enhance the mechanical performance of metallic honeycomb structures. However, there is limited research on the load-rate effects affecting in-plane compression. For the first time, this study investigates the in-plane compressive performance of Steel 316L honeycomb structures produced via material extrusion (ME) and laser powder bed fusion (LPBF). ME honeycombs of three cell sizes and single-cell size LPBF honeycombs were tested under uniaxial compression at varying quasi-static loading rates. Digital image correlation (DIC) was also employed to capture the deformation modes of the honeycombs and to map the local strain fields during compression. Empirical models were used to predict the in-plane compressive performance of the honeycomb structures. Particularly for the plastic collapse stress, an empirical formula incorporating viscoplastic dependency on the cell wall material within the quasi-static loading regime has been derived, producing accurate predictions. Both types of honeycomb structures are load-rate sensitive, as their compressive mechanical properties improved with the load rate increase. Moreover, the variation of the cell size was found to optimise the in-plane compressive performance. The deformation mode for both honeycomb structures was confirmed to be cell wall bending, plastic buckling, cell wall collapse, and folding.

Dynamic response and collapse resistance of RC flat plate structures subjected to instantaneous removal of an interior column

Through quasi-static loading regimes, notable research efforts have been made in recent years towards understanding the structural behaviour and resistance mechanism of reinforced concrete (RC) flat plate structures against progressive collapse events. Nevertheless, dynamic responses, being an inherent nature of any progressive collapse, were unable to be adequately studied in these quasi-static studies. Moreover, fewer studies were performed on flat plate structures under dynamic loading conditions, especially their behaviours under large deformations, i.e., the post-punching stages. To fill this research gap, this paper presents three sequential dynamic tests performed on a 1/3-scaled 2 × 2-bay RC flat plate substructure specimen by instantaneously removing the interior column under three levels of additional gravity loads. In these tests, the substructure specimen was able to withstand the gravity loads up to 2.08 times the load capacities recommended by the DoD and GSA guidelines for nonlinear dynamic analyses. The dynamic responses of the specimen in the flexural, punching and post-punching stages were examined in detail. In addition, a high-fidelity finite element model was developed and validated by the experimental test results. The validated numerical model was subsequently used to quantify the dynamic load redistribution patterns, and the influences of two loading considerations (i.e., loading on the slab overhangs and load release time) on the dynamic responses were also investigated. Finally, the dynamic load increase effects were evaluated based on the analysis model results. The obtained load-based dynamic increase factors (DIFs) of the specimen under different gravity loads were between 1.11 and 1.46 in the pre-punching (flexural) stage, whereas they were no more than 1.06 in the post-punching stage.

An explicit delamination propagation algorithm to simulate delamination growth under quasi-static and fatigue loading without re-meshing using virtual crack closure technique and progressive nodal release

A modeling approach is proposed to simulate delamination propagation in composite laminates under both quasi-static and fatigue loading regimes. Delamination growth is simulated using the Virtual Crack Closure Technique combined with a progressive nodal release strategy. In the proposed approach, the delamination propagation increment is determined explicitly, based on the energy release rate calculated in the previous time increment. Explicitly determining the delamination propagation increment linearizes the system of equations that results from the progressive nodal release strategy and eliminates convergence issues associated with delamination growth. In fatigue, the delamination growth increment is calculated using as input growth rates characterized experimentally via fitting of a suitable form of the Paris law to the experimental data. Under quasi-static loading conditions, a sufficiently large pseudo-growth rate is assumed, such that the simulation results converge to the results obtained with the chosen binary (growth/no growth) fracture criterion. Since both fatigue and quasi-static loading regimes share the same underlying algorithm, simulating the transition between fatigue and quasi-static delamination growth is trivial. The approach is demonstrated to accurately simulate delamination growth for all cases assessed, including quasi-static mixed-mode loading and the transition between fatigue and quasi-static delamination growth regimes. Finally, it is also shown that the approach can simulate both self-similar and non-self-similar delamination growth.

Effects of notch-load interactions on the mechanical performance of 3D printed tool steel 18Ni300

The capability of additive manufacturing to produce parts with complicated geometrical features is one of the unique advantages of this technology over traditional production methods. However, the intricate interaction between concentrated stress fields imposed by various geometrical profiles, inherent defects, and external loads must be comprehensively recognized to leverage the aforementioned ability. Consequently, this study investigated the simultaneous effects of macroscopic notches and microscale defects on the performance of tool steel 18Ni300 under quasi-static and cyclic loading regimes. The specimens were manufactured using the laser-powder bed fusion technique, a common method for industrial applications that rely on metals. Eleven (horizontally built) sample designs, consisting of external or internal notches with different characteristics, were considered in this study to ensure a comprehensive comparison. The results showed that the surface quality was slightly higher along the notch roots than in the other areas. All the notches, regardless of their types, reduced ductility. Notch strengthening was generally observed in the notched samples under quasi-static loads. However, the degree of strengthening was directly related to the stress concentration factor, unlike for typical conventional metals. This unexpected behavior was attributed to the inherent defects in the manufacturing process. The surface defects at the notch roots played a dominant role in governing fatigue failures. A modification of the Murakami approach was proposed to estimate the fatigue life of notched components fabricated via additive manufacturing. Finally, the applicability of the Solberg–Berto diagram to predict the failure locations in horizontally manufactured samples was evaluated. The diagram largely agreed with the experimental data obtained from this study.

Strain rate and size effects on the brittleness indexes of Carrara marble

The determination of rock brittleness is crucial in analyzing excavation efficiency, deep mining stability, geological hazards, while nearly all the previous studies on rock brittleness are conducted in the quasi-static loading regime or based on the quasi-static mechanical properties. But loading rate or strain rate can change the mechanical properties of rocks. In modern engineering, dynamic behaviours of rocks under high strain rates are considered more often. In the past seven decades, various quasi-static brittleness indexes were proposed and studied. However, the size effect on brittleness was not studied comprehensively. For some brittleness indexes, the suggested specimen size is even not given. The present research assesses seven major brittleness indexes by using the dynamic mechanical properties of Carrara marble to check the feasibility of the application of these quasi-static brittleness indexes into the dynamic regime. The size effect is also investigated by using three different specimen dimensions. The results indicate that some quasi-static brittleness indexes, which provide incorrect variation trends of dynamic brittleness, are not applicable in the dynamic regime. Specimen size shows only a limited influence on the dynamic brittleness indexes. Four dynamic brittleness indexes, which have better data stability, reliability and operability, are recommended by the present research.

Nonlinear Mechanical Effect of Free Water on the Dynamic Compressive Strength and Fracture of High-Strength Concrete.

It is well-known that the effect of interstitial fluid on the fracture pattern and strength of saturated high-strength concrete is determined by qualitatively different mechanisms at quasi-static and high strain rate loading. This paper shows that the intermediate range of strain rates (10−4 s−1 < < 100 s−1) is also characterized by the presence of a peculiar mechanism of interstitial water effect on the concrete fracture and compressive strength. Using computer simulations, we have shown that such a mechanism is the competition of two oppositely directed processes: deformation of the pore space, which leads to an increase in pore pressure; and pore fluid flow. The balance of these processes can be effectively characterized by the Darcy number, which generalizes the notion of strain rate to fluid-saturated material. We have found that the dependence of the compressive strength of high-strength concrete on the Darcy number is a decreasing sigmoid function. The parameters of this function are determined by both low-scale (capillary) and large-scale (microscopic) pore subsystems in a concrete matrix. The capillary pore network determines the phenomenon of strain-rate sensitivity of fluid-saturated concrete and logistic form of the dependence of compressive strength on strain rate. Microporosity controls the actual boundary of the quasi-static loading regime for fluid-saturated samples and determines localized fracture patterns. The results of the study are relevant to the design of special-purpose concretes, as well as the assessment of the limits of safe impacts on concrete structural elements.

Non-linear response and buckling of imperfect laminated composite plates under in-plane pulse forces

This study presents a semi-analytical solution of the non-linear dynamic response, shock spectrum, and dynamic buckling of an imperfect angle-ply laminated composite plate under various types of in-plane pulse forces. The laminated composite plate is modeled using a higher-order shear deformation theory and von-Kármán geometric nonlinearity. The non-linear governing partial differential equations (PDEs) of imperfect laminated composite plates are derived via Hamilton’s principle. Using Galerkin’s method, the non-linear PDEs are transformed into non-linear algebraic equations for the static stability problems and non-linear ordinary differential equations for the dynamic problem such as dynamic response, shock spectrum, and dynamic buckling. The buckling load of the plate is obtained through the associated eigenvalue problem. The static failure load of the composite plate is evaluated using the post-buckling analysis based on the Tsai-Wu failure criterion. The dynamic response and shock spectrum of the composite plate are determined via Newmark’s method. The dynamic failure load of the plate is evaluated using Newmark’s method based on the Tsai-Wu failure criterion. Dynamic buckling is to be characterized by dynamic load factor (DLF), which is represented as the ratio of the dynamic failure load to the static failure load. Based on the pulse/shock duration time, the pulse forces are divided into three loading regimes known as impulsive, dynamic, and quasi-static. The study revealed that the DLF values are &gt; 1, &lt; 1, and [Formula: see text]1 respectively for the case of impulsive, dynamic, and quasi-static loading regimes of pulse force. The influences of various types of in-plane pulse forces, amplitude and time duration of pulse forces, and amplitude of initial geometric imperfections on the non-linear dynamic response, shock spectrum, and dynamic buckling behavior of the laminated composite plate are addressed in detail. The results will help in the appropriate design of the laminated composite plate against dynamic buckling.

Nonlinear Response and Buckling of Imperfect Plates Under In-Plane Pulse Forces: A Semi-analytical Investigation

This study presents a semi-analytical solution of the nonlinear dynamic response, shock spectrum, and dynamic buckling of a simply supported imperfect plate under various types of in-plane pulse forces. Here, the plate is modelled based on higher-order shear deformation theory (HSDT) considering the von-Karman geometric nonlinearity. The governing nonlinear partial differential equations (NLPDEs) of the imperfect plates are developed via Hamilton’s principle. Using Galerkin’s method, the NLPDEs are converted into sets of nonlinear algebraic equations (NLAEs) for static stability problems and nonlinear ordinary differential equations (NLODEs) for dynamic problems. The critical buckling load of the plate is obtained through the associated eigenvalue problem. The static failure load of the plate is evaluated using nonlinear static stability analysis based on the yield stress failure criterion. The dynamic response and shock spectrum of the plates are plotted via Newmark’s method. The dynamic failure load of the plate is evaluated using Newmark’s method based on the yield stress failure criterion. Dynamic load factor (DLF) is the ratio of dynamic failure load to static failure load. Based on the pulse duration time, the pulse forces are divided into three categories known as impulsive, dynamic, and quasi-static. In the case of impulsive, dynamic, and quasi-static loading regimes, DLF > 1, DLF < 1, and DLF $$\approx$$ 1, respectively. The results obtained from the current works will help in the appropriate design of the imperfect plates against dynamic buckling.

Dynamic Deformation Behaviour of Chiral Auxetic Lattices at Low and High Strain-Rates

The mechanical behaviour of three different auxetic cellular structures, hexa-chiral 2D, tetra-chiral 2D and tetra-chiral 3D, was experimentally investigated in this study. The structures were produced with the powder bed fusion method (PBF) from an austenitic stainless steel alloy. The fundamental material mechanical properties of the sample structures were determined with classic quasi-static compressive tests, where the deformation process was captured by a high-resolution digital camera. The Split Hopkinson Pressure Bar (SHPB) apparatus was used for dynamic impact testing at two impact velocities to study the strain-rate dependency of the structures. Two synchronised high-speed cameras were used to observe the impact tests. The captured images from both quasi-static and dynamic experiments were processed using a custom digital image correlation (DIC) algorithm to evaluate the displacement/strain fields and the Poisson’s ratio. Predominant auxetic behaviour was observed in all three structures throughout most of the deformation process both under quasi-static and impact loading regimes. The tetra-chiral 2D structure showed the most significant auxetic behaviour. Significant stress enhancement in all tested structures was observed in dynamic testing. The Poisson’s ratio strain-rate dependency was confirmed for all three auxetic structures.

Homogenization of the fluid–structure interaction in acoustics of porous media perfused by viscous fluid

This paper aims to clarify the homogenization results of the fluid–structure interaction in porous structures under the quasi-static and dynamic loading regimes. In the latter case, the acoustic fluctuations yield naturally a linear model which can be introduced in the configuration deformed as the consequence of the steady permanent flow. We consider a Newtonian slightly compressible fluid under the barotropic acoustic approximation. In contrast with usual simplifications, the advection phenomenon of the Navier–Stokes equations is accounted for. The homogenization results are based on the periodic unfolding method combined with the asymptotic expansion technique which provide a straight procedure leading the local problems for corrector functions yielding the effective model parameters and the macroscopic model. We show that the local problems for the solid and fluid parts are decoupled even in the dynamic interactions including the wall shear stress on the periodic interfaces. The dynamic permeability depends on the fluid flow properties including the advection effects associated with an assumed stationary perfusion of the porous structure.

The resilient slip friction joint tension-only brace beyond its ultimate level

The fundamental objective of this research is to investigate the performance of a self-centering tension-only brace beyond its ultimate level. This goal is undertaken by proposing an optimized mechanism to minimize the over-strength factor and maximize the displacement capacity of the system and to experimentally verify this. The proposed mechanism is called secondary-fuse. The investigated tension-only bracing system employs Resilient Slip Friction Joint (RSFJ) at the end(s) of diagonal members to provide self-centering, ductility, and damping with a flag-shape response. Analytical relations are also proposed in conjunction with the experimental results to predict the response. Furthermore, this study presents and discusses the relevant design over-strength factors. Firstly, the over-strength mechanism of the devices is verified through joint component testing. In the next step, the same joints are used in a full-scale two-dimensional steel frame to investigate their behavior on the frame level. The frame is capacity designed in a way that the weak link of the system is RSFJ. Then it is tested under quasi-static loading regime. Based on the test results, the displacement elongation and over-strength factor of three joints, as well as the frame, are given. The parameters affecting the joint elongation are also discussed. To conclude, the test results confirmed that the proposed secondary fuse could well provide the displacement ductility beyond the RSFJ ultimate level while keeping the system self-centered, however, the rods should be replaced after a major event during which the secondary-fuse is activated.

Effects of strain rate on the tensile behavior of cementitious composites made with amorphous metallic fiber

Amorphous metallic fiber has higher tensile strength as well as corrosion and wear resistance than common, crystalline steel fibers. Its utilization as reinforcement improves the crack resistance and flexural and tensile performance of concrete. In the study at hand, the tensile behavior of thin plate amorphous metallic fiber-reinforced cementitious composites (AFRCC) is compared with that of hooked steel fiber-reinforced cementitious composites (HSFRCC) for both quasi-static and dynamic loading regimes. AFRCC exhibites a high stress distribution effect and higher tensile strength, strain capacity, and peak toughness than HSFRCC, but lower tensile toughness and lower dynamic increase factor values for tensile strength, strain capacity, and toughness.

Quasi-static and dynamic behavior of precast concrete frames with high performance dry connections subjected to loss of a penultimate column scenario

Unbonded post-tensioned precast concrete (UPPC) frame exhibits excellent performance in resisting seismic load from experimental tests and post-earthquake investigations. However, the behavior of UPPC frames subjected to extreme load such as the loss of a column due to explosion is still not well studied. To fill this knowledge gap, in this paper, four 1/2 scaled UPPC beam-column substructures were tested under both quasi-static and dynamic loading regimes. The comparative study between these two test-regimes were subsequently performed, which provides a clear understanding of the difference of these two test methods in progressive collapse studies for other researchers. The test results indicated that UPPC frames achieved required load redistribution capacity to mitigate progressive collapse. The failure modes of the frames observed in dynamic test were quite similar to that in quasi-static tests. Moreover, it was found that strain rate effects were insignificant for progressive collapse events caused by suddenly column removal. Based on the measured load resisting function from quasi-static tests, a single-degree-of-freedom (SDOF) model, with the consideration of strain hardening and softening, was developed. After validation, the proposed SDOF model was used to quantify the effects of service load, initial velocity, initial displacements, and damping ratio on the dynamic response. It was found that the damping ratio, non-zero initial velocity and initial displacement are the three most influential parameters.