Impact of corrosion on the compression strength of steel wall ties within a timber-framed brick veneer wall system

The out-of-plane seismic performance of residential brick veneer walls built over wood-frame backup was evaluated as a function of construction detailing. Shake table tests were conducted on a full-scale brick veneer wall panel, with a window opening, representing the gable-end wall of a typical home structure; the structural performance of corrugated sheet metal veneer-to-wood tie connections was also characterized by separate laboratory testing. The wall panel test specimen was prepared following typical construction practice for brick veneer wall systems, in general conformance with current specified prescriptive design and construction requirements. The shake table tests captured the performance of the brick veneer wall system, including interaction and load-sharing between the brick veneer, corrugated sheet metal ties, and wood-frame backup. Detailed three-dimensional finite-element (FE) models were also developed representing the full-scale brick veneer wall panel specimen, including nonlinear inelastic properties for the tie connections. After calibration based on test results, the FE wall panel model effectively captured static and dynamic experimental brick veneer wall behavior at different response levels, up to and including tie damage and even instability/collapse of the wall panel. Parametric studies were then carried out using FE wall panel models to evaluate the effects of certain types and layouts of tie connections, as well as geometric variations in brick veneer wall construction. Overall seismic performance of brick veneer walls was closely related to the individual tie connection deformation limits, especially for damage in tension. The grid spacing of tie connections, as well as tie installation along the edges and in upper regions of the walls, controlled the ultimate behavior of the brick veneer wall panels. Design guides, codes, and current construction practices have been evaluated in light of the overall findings from these experimental and analytical studies.

Wall ties are a metal fitment used in masonry walls that provide an important connection between the external leaf of masonry and the internal wall or frame. In a cavity brick wall, the internal wall is masonry, mirroring the external wall, with an air cavity in between. The wall tie is embedded in both leaves of masonry and, in the event of strong winds or an earthquake, transfers lateral loads between them. Inevitably, the wall ties experience losses due to corrosion mechanisms occurring within the microenvironments of the cavity wall. The impact corrosion losses have on the behaviour of the wall ties in tension and compression are useful for understanding when a cavity brick wall might be vulnerable to collapse. The present study reports on the axial tension and compression testing results of cavity brick wall subassemblies, comparing the findings of non-corroded and artificially corroded wall ties. Subassembly specimens represent a single connection, and hence numerical models were also completed to show the behaviour of the cavity wall when corrosion losses are induced to the wall ties within a full-scale wall.

Wall ties or masonry veneer anchors are a common part of brick veneer wall assembly construction. They serve to anchor the brick veneer to the backup wall, whether that is a wood-stud, steel-stud, or concrete block wall. They provide structural support and keep the brick veneer from moving. However, since wall ties are made from steel, they have a significantly higher thermal conductivity than the surrounding materials in the building envelope, and this difference may cause thermal bridging. The overall impacts of several common types of wall ties in residential and commercial construction were tested using a small-scale hot box apparatus under steady-state conditions. Each test panel was first tested without any wall ties and then subsequently tested with wall ties present. This procedure allowed for direct measurement of the impact of the wall tie while holding all other factors constant. In the case of a typical residential wall without continuous insulation, both types of wall ties tested were found to have no measurable impact on the overall thermal performance. In the commercial walls that contained continuous insulation, the walls ties were found to have a minor impact on the overall thermal performance. Wall systems with significant thermal mass, such as brick veneer, have better performance under dynamic thermal loading, which is not reflected in steady-state measurements. This paper focused on steady-state worst-case results, and future work will address dynamic performance.

This chapter defines terminology and construction methods for brick masonry chimneys, veneer walls, porches, and decks. It describes typical mechanisms and causes associated with the failure of brick masonry chimneys, veneer walls, porches, and decks. Masonry construction is widely used to build various structures, including houses, pathways, steps, decks, porches, and chimneys. Mortar is a malleable paste used to bind masonry units together and is typically composed of sand, water, and a binder. The performance of a masonry chimney or veneer wall is directly related to both limiting the amount of water/moisture penetration and controlling or managing the water/moisture that does enter through the brick masonry. The most common issue encountered in forensic field investigations for the failure of a chimney is associated with the footings where the chimney appears to have rotated away from the structure. Information regarding chimney construction requirements can be found in most modern residential and commercial building codes and in best practice documents.

Out-of-plane seismic performance and fragility analysis of anchored brick veneer

A study of the out-of-plane performance of brick veneer wall systems in medium rise buildings under seismic loads

This paper reports the first part of an ongoing research project that is looking into the seismic performance of veneer walls. The type of veneer of interest for this work is normally anchored to the backup wall through metal ties. Brick veneer walls are supported in most cases by shelf angles attached to the floor slab at each story and are supposed to carry only their own weight and not participate in in-plane lateral load resistance. To achieve this behavior, horizontal and vertical movement joints are necessary. Ideally, this design could isolate the lateral movement of the backup wall from that of the veneer wall, thus preventing any distress to the veneer. However, earthquake reconnaissance reports show many failures of veneer walls with the potential of life-safety hazard. In this paper, it is discussed how the vertical differential movement between the brick veneer and the frame can close the gap between the underside of the shelf angle and the top course of brick, thus putting the brick veneer under high compressive stresses. It is shown that this can result in proportionally high friction forces during earthquakes with the possibility of shear cracking of the veneer before sliding between the brick veneer and the supporting steel shelf angle occurs.

Evaluation of code provisions for design of medium rise buildings supporting brick veneer wall systems under the effect of in-plane seismic loads

Out-of-plane performance of brick veneer walls on wood frame construction

There has been a significant effort to design and construct multi-hazard resistant buildings in recent years, but the emphasis has been more on structural systems. A study has been undergoing at The Pennsylvania State University to develop a multi-hazard resistant brick veneer wall system, normally considered a nonstructural component as it does not participate in gravity or lateral load resisting system. However, since brick veneer walls are part of the building envelope system, they are quite vulnerable to various loading regimes. The study reported in this paper is an enhancement of an original concept that developed a panelized brick veneer over steel stud wall system to resist high wind and seismic effects. The enhancement concepts discussed are aimed at providing improved performance under extreme out-of-plane loading conditions. Full-scale static air bladder pressure tests were performed on four different mockups to investigate the beneficial effects of seismic veneer anchor ties, steel reinforcement in the brick veneer, use of sheet metal over steel studs, and use of composite sheet metal/gypsum boards as sheathing over steel studs. Details of the testing program and experimental results are presented. It is shown that the enhancement techniques result in a modest increase in strength and good composite action between the brick veneer and the combination of steel stud and the sheathings added.

The evaluation of seismic vulnerability of existing buildings with masonry veneer systems has been recognized as a major problem because of the large number of buildings constructed before the development of rational seismic codes. This resulted in the construction of masonry veneers without reference to the design to seismic action and adequate constructive detailing. In order to contribute to increasing of knowledge about seismic behaviour of brick veneer walls, an experimental campaign was developed on testing quasi-statically full-scale systems under in-plane and out-of-plane loading. This paper describes in detail the out-of-plane performance of a constructive system characteristic of Portugal and South of Europe, constituted of brick masonry veneer leaf connected to an infill wall inserted in a reinforced concrete (rc) frame. A description of the test setup for the out-of-plane tests is provided and the main results, including the damage patterns and force displacement diagrams, are presented and discussed.

Canada employs a prescriptive-based code for residential buildings. The minimum requirements as prescribed in the 2015 National Building Code were developed based on historical climate which was assumed static. It is now evident that the climate is changing and it is anticipated that wind-driven rain events will be more frequent, of longer duration and of increased intensity. These changes may affect the durability of wall assemblies designed following the minimum requirements set in the building code. In this study, the moisture performance of residential wood-framed walls using brick veneer as cladding and meeting the minimum requirements of the National Building Code were evaluated for different climatic regions of Canada. Various types of brick veneer were evaluated using hygrothermal simulations and projected future climate loads. The mold growth index on the sheathing panel was used as performance indicator. Results showed that the future moisture performance of brick veneer walls depends on the brick properties and varies with climatic region. In particular, for brick veneer having relatively high water absorption coefficient and lower vapor permeability, there may be a heightened risk to mold growth in the future if used in locations on the east and west coasts of Canada. As consequence, the minimum requirements for brick veneer walls may need to be reviewed in these locations to ensure their long-term performance.

Seismic response of a new type of masonry tie used in brick veneer walls

The Masonry Standards Joint Committee (MSJC) Building Code Requirements for Masonry Structures currently requires a W1.7 gauge continuous, single-wire joint reinforcement at a maximum spacing of 18 in. (450 mm) O.C. vertically be provided in Seismic Design Categories (SDC) E and F. The purpose of this paper is to investigate the justification for this requirement and to determine its necessity. Previous research and testing have been studied, and in-plane and out-of-plane analyses have been completed. Finally an experimental program was designed to determine the effects of joint reinforcement on the brick veneer wall system.

Analysis of brick veneer walls on wood frame construction subjected to out-of-plane loads