Experimental and Numerical Study of Composite Lightweight Structural Insulated Panel with Expanded Polystyrene Core against Windborne Debris Impacts

Natural disasters such as cyclone, hurricane, tornado and typhoon cause tremendous loss around the world. The windborne debris usually imposes high speed localized impact on the building envelope, which may harm people inside the building and create dominant openings. A dominant opening in the building envelope might cause internal pressure increasing and result in substantial damage to the building structures, such as roof lifting up or even collapse. To withstand the impact of such extreme event, the penetration resistant capacity of wall or roof panels to windborne debris impact should meet the requirements specified in the wind loading codes, e.g., the Australian Wind Loading Code (AS/NZS 1170.2:2011). In this study, a composite Structural Insulated Panel (SIP) with Extended Polystyrene (EPS) core sandwiched by flat metal skins that is commonly used in building industry was investigated. To study the structural response and penetration resistant capacity of the composite panel against windborne debris impacts, a series of laboratory tests were carried out by using a pneumatic cannon testing system.The effects of various specimen configurations, impact locations and debris impact velocities on their performance were investigated. The failure modes under various projectile impact scenarios were observed and compared by using two high-speed cameras. The dynamic responses were examined quantitatively in terms of the opening size, residual velocity of projectile, deformation and strain time histories on the back skin measured in the tests. The penetration resistance capacity of the panels subjected to windborne debris impact were examined and analyzed. In addition, numerical models were developed in LS-DYNA to simulate the response and damage of the composite SIP under windborne debris impact. Laboratory tested panels were first modeled. The test data was used to calibrate the accuracy of the numerical model. The validated numerical model was then used to conduct more numerical simulations to obtain more results such as energy absorption, impact force and vulnerability curve of the SIP against windborne debris impact

Fragility curves for corrugated structural panel subjected to windborne debris impact

With the climate change, more and more extreme wind events such as cyclone take place around Australia and the world, which cause tremendous loss and damage. The wind speed has been reported constantly increasing with the climate change, which imposes more threats to building environments. The building envelopes are vulnerable to the windborne debris impact in a form of creating an opening in wall, roof, door, windows and screens, which leads to internal pressure increase and results in roof lifting up. The capacity requirements of wall or roof panels to resist windborne debris impact in cyclonic regions has been substantially increased in the 2011 Australian Wind Loading Code (AS/NZS 1170.2:2011) as compared to its previous version. The performance of commonly used structural panels in Australian Building Industry under the increased design wind speed needs be evaluated. Intensive laboratory tests and intensive numerical simulations on performances of typical structural panels subjected to windborne debris impacts have been carried out. This paper presents the results of one panel type, i.e., corrugated panel. The vulnerability curves of the corrugated panel with respect to the debris mass and impact speed are simulated. These results can be used in probabilistic loss estimations of structural panels in extreme wind events

Impact response and energy absorption of single phase syntactic foam

© 2018 Elsevier Ltd. This study experimentally investigates the static and impact response of a new single phase syntactic foam which has been newly developed for impact energy absorption. The syntactic foam had different densities ranging from 172 kg/m3to 366 kg/m3depending on the thickness and composition of the coating layers. The impact response and impact energy absorption were investigated by using instrumented drop-weight impact tests. Under static loads, the mechanical properties of the syntactic foam including the compressive strength, the yield stress, and Young's modulus increased with the density but the rate of increment decreased at higher densities. There were two types of progressive failures of the syntactic foam under impact loads. The failure propagation was examined and found to be dependent on the material density and the impact velocity. Interestingly, the densification only occurred in the low-density specimens while this phenomenon was not observed for the specimens with the density greater than 288 kg/m3. The impact energy absorption capacity increased significantly with the density and the wall thickness of the macrospheres

Effect of crumb rubber on mechanical properties of multi-phase syntactic foams

Syntactic foam is a lightweight and strong material which can be used in marine and aeronautical applications. However, the brittleness of the material limits its application to a broader range. Adding crumb rubber to the syntactic foam can increase its energy absorption capacity. The effect of crumb rubber on the fracture toughness and energy absorption capacity of 2-phase and 3-phase syntactic foam is evaluated under both static and impact loads. The experimental results have shown that the fracture toughness of the 2-phase rubberized syntactic foam increased by 8% while an increase of 22% of its fracture energy was observed. Under quasi-static loads, the 3-phase rubberized syntactic foam showed decreases in the compressive strength and elastic modulus but an increase in the energy absorption capacity as compared to the syntactic foam without crumb rubber. In addition, the impact energy absorption of the 3-phase rubberized syntactic foam increased by 24% as compared to that of the 3-phase syntactic foam without crumb rubber

Review on impact response of reinforced concrete beams: Contemporary understanding and unsolved problems

Designing protective reinforced concrete (RC) beams against impact loadings is a challenging task. It requires a comprehensive understanding of the structural response of RC beams subjected to impact loads. Significant research efforts have been spent to unveil the impact response of RC beams by using analytical models, experimental testing, or numerical investigations. However, these studies used various assumptions in the analytical derivations and different test setups in the impact testing, which led to significantly different responses and observations of similar structures and similar loading conditions. For example, a minor change in contact surface can triple the maximum impact force of identical RC beams. This study provides a review of the contemporary understandings of the RC beam responses to impact loads, and explains the different observations and conclusions. Some unsolved issues for protective structures, that is, RC beams to resist impulsive loads are also discussed. It is suggested that future studies should take into consideration the conditions of the test setup, simplifications and assumptions made in analytical derivations for better interpretations of the obtained results

Functionally graded truncated square pyramid folded structures with foam filler under dynamic crushing

Dynamic crushing responses and energy absorption of functionally graded folded structures with foam fillers are investigated in this study. The proposed structure consists of multiple layers of folded truncated square pyramid (TSP) foldcore with foam fillers added inside each unit cells and the interlayer plates to separate each layer of foldcore and its foam filler. The foldcores are folded using pre-patterned thin aluminium sheets. Two types of foam including cubic shape expanded polystyrene (EPS) foam fillers with density of 13.5, 19 and 28 kg/m3 and rigid polyurethane (PU) foam of 35 kg/m3 with two shapes. Two sets of functionally graded multi-layer structures are achieved by varying the densities of EPS foam fillers (positively/negatively graded EPS) and varying the shapes of PU foam fillers (positively/negatively graded PU) inside each layer of TSP foldcore. These specimens are then crushed under 1 and 10 m/s. Under 1 m/s crushing, excellent crushing responses as energy absorber are observed for both negatively graded and positively graded multi-layer structures with low initial peak force and low fluctuation in resistance throughout deformation. Under 10 m/s crushing, however, positively graded structures show much more uniform load-displacement response with significantly reduced peak crushing force, increased energy absorption than negatively graded structures. Up to 60% increase in specific energy absorption is shown for folded structure with positively graded PU foam as comparing to the uniform structure without foam filler under 10 m/s crushing

Numerical study on bending response of precast segmental concrete beams externally prestressed with FRP tendons

This study numerically investigates the bending response of dry key-jointed precast segmental concrete girders/beams (PSCBs) prestressed with external fiber reinforced polymer (FRP) tendons by using commercial finite element analysis (FEA) software Abaqus/CAE. The experimentally-validated model was used to conduct an intensive parametric analysis with a focus on the second-order effect. There has not been a similar numerical study of PSCBs with external FRP tendons in the published literature yet. The results showed that due to the rectilinear rigid-body bending shape, the behavior of PSCBs with external tendons was similar to that with internal tendons only if placing the deviators next to the opening joints. The second-order effect on the beam's behavior and the harping effect on the tendon stress at deviators became more obvious when the deviators were located away from the opening joints. Both the second-order and harping effect were proportionate to the beam's displacement. Therefore, using a high reinforcing index (ω) or a low span-to-depth ratio (L/dp) could mitigate the second-order and harping effect at the ultimate stage because the ultimate displacement of the beam decreased when increasing ω or reducing L/dp. Commonly-used CFRP tendons (Young's modulus Ep = 145 GPa) were found to be the optimum to replace steel tendons in PSCBs with external tendons because they offered the PSCBs similar strength and ductility compared to steel tendons. The use of high-modulus CFRP tendons (e.g. Ep = 200 GPa) improved the stiffness and strength of PSCBs but greatly reduced the beam's ductility. Lastly, the analytical analyses showed that the existing models yielded unconservative estimations of the effective depth (dpu) and stress (fpu) of external FRP tendons at the ultimate stage in PSCBs

Spall Behaviors of Metaconcrete: 3D Meso-Scale Modelling

Spalling is a typical tensile fracture phenomenon due to insufficient tensile strength of concrete. Concrete structure might experience severe spall damage at the rear surface of the structure owing to reflected tensile stress wave induced by impulsive load. In recent years, metaconcrete consisting of engineered aggregates has attracted attentions as metaconcrete exhibits extraordinary wave-filtering characteristics. Metaconcrete can be used to attenuate stress wave generated by impulsive load and hence possibly mitigate the spall damage. In this study, engineered aggregate is designed via the software COMSOL to have the frequency bandgap coincide with the dominant frequency band of stress wave propagating in the normal concrete (NC) specimen to reduce the stress wave propagation and hence spall damage. The wave propagation behaviors in metaconcrete specimen with periodically distributed engineered aggregates have been investigated in a previous study. This study establishes 3D meso-scale model of metaconcrete including mortar, randomly distributed natural aggregates and engineered aggregates to simulate spall behaviors of metaconcrete via the software LS-DYNA. The responses of metaconcrete composed of engineered aggregates with single bandgap and multiple bandgaps are studied. The results show that stress wave can be more effectively attenuated by using engineered aggregates with multiple bandgaps. It is found that although engineered aggregates mitigate stress wave propagation, the soft coating of the engineered aggregates reduces the concrete material strength, therefore spall damage of metaconcrete specimen is not necessarily less severe than the normal concrete, but has different damage mode. In addition, the influences of loading intensity and duration on stress wave, as well as the spall behaviors of metaconcrete specimen are also studied

Predicting the response of locally resonant concrete structure under blast load

Ternary locally resonant metamaterial (LRM) is a manmade material consisting of rigorously designed heavy inclusions with coated soft layer. Such design enables the LRM to possess good wave-filtering characteristics that differ from the matrix materials. Researches of application of this new material for seismic isolation and sound insulation in civil engineering have been reported. In recent decades, there has been an increasing demand to protect civil engineering structures against the effects of blast loading. When blast wave acts on a concrete structure, complex stress waves are generated and propagate in the structure. The wave-filtering characteristics of LRM have brought inspiration to investigate its potential application to reduce the stress wave propagation and hence the damage to cementitious material and enhance the performance of structures under blast wave. By embedding heavy inclusions with soft coating layer into mortar matrix, the product can be named as ternary locally resonant concrete (ternary LRC). Previous studies of the performances of ternary LRC structures are mainly limited to finite element (FE) modeling of elastic wave propagation. The study of the performance of ternary LRC structure subjected to blast loading and the influence of blast loading-induced damage to LRC structure on stress wave propagation is very limited. This paper carries out analytical derivation and numerical modelling to study the mechanism and performance of ternary LRC structure under blast loading. The strain rate effect and material damage of the mortar matrix are considered in numerical simulation. The influence of different material inclusions (natural aggregates and lead), different elastic modulus and thickness of the soft coating on the response of ternary LRC structure are studied. The results show that the ternary LRC can effectively reduce the damage of ternary LRC structure subjected to blast loading

Effect of enhanced coating layer on the bandgap characteristics and response of metaconcrete

Metaconcrete is made by partially or fully replacing natural coarse aggregates (NA) in normal concrete (NC) with engineered aggregates (EA). Normal engineered aggregate (NEA) is made by wrapping elastic coating outside spherical heavy core. It was found that mixing NEA in concrete could effectively mitigate stress wave propagation in metaconcrete structure owing to the local resonance of the heavy core of NEA. However, it also reduced the concrete material stiffness and strength because of the low modulus of soft coating that led to relatively large deformation of mortar matrix under loading. To address the issue of low interface stiffness while maintain the local vibration ability of NEA, new enhanced engineered aggregate (EEA) is proposed by placing an additional enhanced coating layer outside the soft coating of NEA. In this study, three types of EEA aggregates composed of three enhanced coating layer materials (i.e., epoxy resin, steel, ultra-high performance concrete UHPC) are considered and their configurations are designed via the software COMSOL. The spall behaviors of enhanced metaconcrete (EMC) mixed with EEA aggregates are examined though numerical simulations. 3D mesoscale models of EMC composed of mortar, randomly distributed natural aggregates and EEA aggregates are built via the software LS-DYNA. The distinction between the bandgap characteristics of NEA and EEA is studied. The effects of enhanced coating layer material on the bandgap of EEA and the performance of EMC with respect to energy absorption capacity, wave attenuation characteristics, and spall strength are studied. The results show that the existence of enhanced coating layer slightly affects the bandgap characteristics of engineered aggregate. Applying an additional stiffer coating layer to make the EEA aggregates can improve the spall strength of metaconcrete mixed with EEA aggregates while its ability in mitigating stress wave propagation and energy absorption is only slightly affected