رفتار ساختاری و مدل سازی در مقیاس کامل پانل های دیوار عایق شده سازه کامپوزیت
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|28750||2012||15 صفحه PDF||سفارش دهید||9230 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Engineering Structures, Volume 41, August 2012, Pages 320–334
This paper investigates the structural behavior of a new type of Composite Structural Insulated Panels (CSIPs) for load-bearing wall applications. The proposed composite panel is made of low cost orthotropic thermoplastic glass/polypropylene (glass-PP) laminate as a facesheet and Expanded Polystyrene Foam (EPS) as a core. The proposed CSIP wall is intended to overcome problems of the traditional Structural Insulated Panels (SIPs). These problems include termite attack, disintegration due to flood water, mold buildups and poor penetration resistance against wind borne debris. Full scale experimental testing for three CSIP panels was conducted to study the behavior of CSIP walls under eccentric load. Further, pull off strength tests were conducted to determine the bonding strength between the glass-PP facesheet and EPS foam core. Facesheet/core debonding was observed to be the general mode of failure. This study provides also analytical models to predict the interfacial tensile stress at the core/facesheet interface, critical wrinkling stress and deflections for a structural CSIP wall member. In addition, finite element modeling was also conducted using ANSYS software in order to model the response of CSIPs walls under in-plane loading. Experimental results were validated using the proposed analytical models and FE modeling, and were observed to be in good agreement. Furthermore, a parametric FE study was conducted to investigate the influence of key design parameters on the behavior of CSIPs. The study showed that span-to-depth ratio and core density have a significant effect on the structural performance of CSIP wall panels.
Traditional Structural Insulated Panels (SIPs) are made of wood-based facing and foam core. These SIPs are often subjected to termite attack, mold buildups, rotting and have poor penetration resistance against wind borne debris. So the need for an effective alternative became an urgency. Composites are a great candidate to replace the traditional panels for housing applications. This paper presents a new composite panel system: Composite Structural Insulated Panels (CSIPs) which were developed by the authors. CSIPs are made of low cost orthotropic thermoplastic glass/polypropylene (glass-PP) laminate as facesheets and Expanded Polystyrene Foam (EPS) as a core. CSIPs take the concept of the sandwich construction that consists of two strong, thin facings and a soft lightweight thicker core. The facesheets carry the bending stresses while the thick core resists the shear loads and stabilizes the faces against bulking or wrinkling . The core also increases the stiffness of the structure by holding the facesheets apart. Core materials normally have lower mechanical properties compared to those of facesheets. Despite the high strength resulting from this combination, deflection and debonding are other significant aspects that are considered in the design of CSIPs . Several investigations have been conducted at the University of Alabama at Birmingham (UAB) by the authors and others on developing composite panels for building applications using rigid and soft cores with thermoset and thermoplastic facesheets , , , , ,  and . It was demonstrated by these studies that the developed panels can provide much higher strength, stiffness, and creep resistance than traditional ones that are made with wood-based facing. The developed CSIPs have a very high facesheet/core moduli ratio (Ef/Ec = 12,500) compared with the ordinary sandwich construction where the ratio is normally limited to 1000 . Further, CSIPs are characterized by low cost, high strength to weight ratio, and lower skill required for field construction, etc. These panels can be used for different elements in the structure, including structural elements (e.g., load bearing walls, floors, and roofs) and non-structural elements (e.g., non-load bearing walls, lintels, and partitions). Many theoretical and experimental studies have been conducted on sandwich construction to investigate their behavior under different types of loadings including in-plane and out-of-plane loadings. A general review of failure modes of composite sandwich beams construction was given by Daniel et al.  while those of sandwich wall were given by Gdoutos et al. . Failures modes for sandwich beams include yielding of facesheet in tension, core shear failure, and local buckling of facesheet in compression which is known as wrinkling of facesheets. Failure modes of sandwich wall include global buckling, local buckling “wrinkling”, and core failure. In case of global buckling, the core may exhibit a substantial shearing deformation whereas in case of local buckling the core acts as an elastic foundation for the facesheets in compression  and . The local buckling can be outward or downward. Outward buckling is known as debonding whereas downward buckling is known as core crushing. The former occurs in case of a sandwich panel with closed cell cores (e.g., EPS foam) while the latter is more characteristic of sandwich panels with open cell cores (e.g., honeycomb core) . Among the first to study the behavior of sandwich panels were Gough et al.  and Hoff and Mautner . They tested sandwich specimens under compressive loading and observed that the general mode of failure was facesheet wrinkling. They also developed formulas to predict the stress in the facesheet at wrinkling. These formulas were then modified to fit the experimental results. The results showed that the wrinkling stress is independent of loading and boundary condition and mainly depends on the facesheets and core moduli. The objectives of the current work are: to investigate the structural behavior of full scale CSIP walls under eccentric loading; to develop models to determine stresses associated with debonding, and to develop a model for equivalent CSIP wall stiffness considering the core deformation effects to determine the deflection of a CSIP wall member.
نتیجه گیری انگلیسی
The behavior of a new type of composite panels (CSIPs) for structural wall applications was investigated under eccentric compressive loading. Analytical and finite element models were also provided to model this behavior. In addition, a parametric finite elements study was conducted to investigate the key design parameters on the behavior of CSIP wall panels. The parameters considered were span-to-depth ratio and core density. The following conclusions are drawn from this study: 1. CSIPs panels failed by localized debonding between the core and facesheets in the maximum compression side with natural half-wavelength equal to the core thickness. This mode of failure is known as wrinkling of the facesheet in compression which is caused by a sudden local buckling of the facesheets. This mode is mainly because the out-of-plane interfacial stress exceeded the core tensile strength. This was demonstrated also by the pull off strength tests. 2. The behavior of the panels was linearly elastic till the onset of debonding. After the initiation of debonding, panels showed a decrease in the stiffness and this was observed from the change of the slopes of the load–deflection curves. 3. Despite the debonding, CSIPs wall panels satisfied both design load and deflection limit as provided by APA design guide and ACI-318, respectively. In other words, they have satisfied both strength and stiffness criteria required for design of a structural sandwich panel. 4. A model for the interfacial facesheet/core out-of-plane tensile stress was developed and validated by demonstrating the close proximity to the experimental results. The results proved that the predicted interfacial stress is higher than core tensile strength and therefore, debonding was the general mode of failure. This validates the criteria that the interfacial stress in independent of loading and boundary conditions and depends only on the core properties. 5. The proposed theoretical model for the critical wrinkling stress based on the Winkler foundation model less conservatively predicted the actual wrinkling stress. Accordingly, an empirical formula in Eq. (22) was proposed to predict the critical wrinkling stress at the debonding for CSIP wall panels considering the orthotropic facesheets with Pn = σcr · b · t. 6. A formula for equivalent stiffness of sandwich wall panel with orthotropic facesheet and solid core was developed to take into consideration the effect of core deformation. This formula is used to determine the deflection of sandwich wall. The close convergence between the experimental and theoretical deflections validates this formula. 7. The reasonable agreement between the analytical and finite element models and experimental results for CSIP walls illustrates that the analytical model accurately predicts the performance of the panel and is likely to minimize full scale tests of panels for code acceptance. In addition, a modeling tool would also allow the behavior of the panels to be investigated under different load combinations. 8. Parametric study developed using FE modeling showed that the span-to-depth ratio is an effective parameter for both deflection and compressive strain in the facesheet whereas the core density has a significant influence on the deflection and very little effect on the compressive strain of the facesheet. The deflection decreased by 70% due to changing the core density from 1 PCF to 3 PCF whereas as a small reduction in strain (about 3%) was obtained. This is because the strain depends mainly on the dimensions and thicknesses of both core and facesheet not on the core rigidity.