This paper presents a shake‐table test study to investigate the displacement capacity of shear‐dominated reinforced masonry wall systems and the influence of wall flanges and planar walls perpendicular to the direction of shaking (out‐of‐plane walls) on the seismic performance of a wall system. Two full‐scale, single‐story, fully grouted, reinforced masonry wall specimens were tested to the verge of collapse. Each specimen had two T‐walls as the seismic force‐resisting elements and a stiff roof diaphragm. The second specimen had six additional planar walls perpendicular to the direction of shaking. The two specimens reached maximum roof drift ratios of 17% and 13%, without collapsing. The high displacement capacities can be largely attributed to the presence of wall flanges and, for the second specimen, also the out‐of‐plane walls, which provided an alternative load path to carry the gravity load when the webs of the T‐walls had been severely damaged. The second specimen developed a higher lateral resistance than the first owing to the additional axial compression exerted on the T‐walls by the out‐of‐plane walls when the former rocked. The shear resistance of the T‐walls evaluated with the design code formula matches the test result well when this additional axial compression is taken into account. However, it must be understood that the beneficial influence of the wall flanges depends on the magnitude of the gravity load because of the P‐Δ effect and the severity of damage induced in the wall flanges when the wall system is subjected to bidirectional ground motions.
Damage assessment of wood frame shear walls subjected to lateral wind load and windborne debris impact
A number of studies have been performed to understand the lateral load carrying capacity of wood frame shear walls. The existing studies, however, have been primarily focused on the intact shear walls, disregarding the possibility of capacity loss due to prior extreme loading events. During windstorms, in particular, windborne debris is the leading cause of damage and destruction. While the impact force induced by windborne debris can directly damage a shear wall, the consequences can become disastrous, as the prior damage adversely affects the in-plane lateral load carrying capacity of the shear wall. This critical aspect motivated the current study to investigate the impact and post-impact performance of wood frame shear walls. For this purpose, a high-fidelity computational framework capable of characterizing both types of damage is developed. Further to providing an in-depth understanding of the process of damage formation and propagation, this study examines how a range of impact scenarios and wall design factors influence the extent of damage that the wood frame shear walls experience in a windstorm. The outcome of this study is then employed to introduce a capacity loss index for the multi-hazard design and assessment of wood frame (and other similar) shear walls in the regions prone to severe windstorms.
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- NSF-PAR ID:
- 10176377
- Date Published:
- Journal Name:
- Journal of wind engineering and industrial aerodynamics
- Volume:
- 198
- ISSN:
- 0167-6105
- Page Range / eLocation ID:
- 104091
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary -
Blass, Hans (Ed.)Wood buildings in North American has been predominantly constructed using light-framed wood systems since early 1900’s, with only limited exception of heavy timber construction in some non-residential applications. This situation is likely to change in the future with the growing acceptance of mass timber construction in the region. In fact, a number of mass timber buildings have been constructed in recent years in the U.S. and Canada, including low- to mid-rise mixed-use buildings (e.g. UMass Student Center, T3 building) and tall towers (e.g. Brocks Commons at UBC). Most of these buildings utilized cross laminated timber (CLT) or nail laminated timber (NLT) floors and heavy timber framing systems to support gravity loads, and a non-wood lateral system such as concrete shear walls or a braced steel frame to resist wind and seismic loads. Although CLT material and glulam products have been recognized in the U.S. and Canada (IBC (2018) and NBCC (2015), there is currently no mass timber lateral systems in the U.S. and only one system (platform style panelized CLT shear wall) in Canada that is currently recognized by the building codes. As a result, special design procedures and review/approval processes must be followed for any building intended to use a mass timber lateral system. There is a need to promote codification of mass timber lateral systems in order to help further develop mass timber building market in North American. At the time of this paper, there has been an on-going effort to devel-op seismic design parameters for panelized CLT shear walls in the U.S. (ref) following the FEMA P695 procedure for platform construction. The other lateral system that at-tracted significant attention and research resources is post-tensioned CLT rocking wall system, which has the potential to be applicable to balloon framed low-rise to tall wood buildings. This paper will focus on recent research development on CLT rocking wall system in the U.S. and the effort to develop a seismic design procedure for this system for inclusion in the NDS Special Design Provisions for Wind and Seismic (SPDWS)(2008). While the expensive and time consuming process of the FEMA P695 process would provide the ability to use the equivalent lateral force method for design purposes, this path is not part of the discussion included here.more » « less
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To meet the increasing demand for high strength and non-combustible shear wall systems in mid-rise cold-formed steel (CFS) constructions, this paper investigates the seismic performance and design method of an innovative CFS shear wall system with in-frame corrugated steel sheathing based on previous studies. Shear wall and bearing wall specimens with in-frame corrugated steel sheathing are tested under combined lateral and gravity loading. Simplified numerical models of whole archetype buildings are established. The seismic performance evaluation is performed using methodology recommended in FEMA P695 and the seismic performance factors are examined. The test results show that the shear strength of the innovative shear wall is much higher than currently code certified wood-based shear walls in AISI S400. Also, the shear strength of bearing walls is approximately one-third of the shear strength of shear walls, which proves that bearing walls also contribute significant shear resistance in a structure. The seismic performance evaluation results verified that the existing seismic performance factors (R = Cd = 6.5 and [Formula: see text] = 3.0) for CFS shear walls with flat steel sheathings can also be used for the innovative shear wall system. The innovative CFS shear wall system with in-frame corrugated steel sheathing could be employed for mid-rise buildings in areas that are prone to high seismic and wind loads.
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Modern seismic resistant design has been focusing on development of cost effective structural systems which experience minimal damage during an earthquake. Unbonded post-tensioned precast concrete walls provide a suitable solution due to their self-centering behavior and their ability to undergo large nonlinear deformation with minimal damage. Several experimental and analytical investigation focusing on lateral load resisting behavior of unbonded post-tensioned precast walls has been carried out in the past two decades. These investigations have primarily focused on lateral load resistance, self-centering capacity, energy dissipation and extent of damage in confined concrete region of the wall system. Past experimental results have shown that self-centering capacity of the wall system decreases at higher lateral drifts. Particularly, rocking walls with higher energy dissipation capacity, sustain considerable residual displacement. This residual displacement in the wall system may affect the ability of the entire structure to re-center. Though increasing initial prestressing force helps in reducing residual drift, it also subjects concrete to increased axial compressive stress which may lead to premature strength degradation of confined concrete in rocking corners. Accurate prediction of expected concrete strains in confined regions during increasing drift cycle is critical in design of such wall systems. Simplified design procedures available in literature assume different values for plastic hinge length to estimate critical concrete strain values. The results from the experimental tests available in literature were analyzed, to understand the effects of energy dissipating elements on residual drift and to examine the accuracy of simplified design procedures in predicting critical concrete strain. Based on the findings, recommendations are made on design of energy dissipating elements and plastic hinge length for unbonded post-tensioned precast rocking walls.more » « less
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Structural Insulated Panels (SIPs), which consist of a composite of an insulating polymer foam sandwiched between two layers of structural skins, are widely used in residential and commercial buildings. Such panels, in the regions prone to hurricanes and tornadoes, are often exposed to the risk of windborne debris impact. Despite the consequences associated with damage to SIPs, the studies on their perforation resistance and design variables have been rather limited. To address this gap, the current study develops a computational framework to assess the vulnerability of the SIPs of various configurations subjected to a range of windborne debris impact scenarios. For this purpose, impact simulations are conducted to quantify the response and evaluate the extent of damage to the SIPs. The study is further extended to evaluate the effect of various structural details and material properties on the perforation resistance of the SIPs. Based on the simulation results, a set of vulnerability curves are developed for the first time to capture the risk of failure of the SIPs under the windborne debris hazard. This is expected to improve the design of this important category of wall panels, especially to ensure their safety and performance during severe windstorms.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.jweia.2020.104091
