Steel Roof Battens Research Articles

Design of thin steel battens subject to pull-through failures

Localized pull-through failures of cold-formed steel roof battens have often been observed at the roof batten to purlin/rafter/truss screw connections during storms and cyclones. Recent research studies have therefore proposed improved design capacity equations by undertaking both experimental studies and finite element analyses. However, they have not investigated the effects of very thin steel roof and ceiling battens (<0.50 mm), safety lip features and purlin flexibility on the localized pull-through failures. Hence this study was aimed at investigating the effects of all such practical design issues and to assess the suitability of current design equations. For this purpose, a series of static and fatigue pull-through failure tests of roof and ceiling battens was undertaken under simulated static and cyclic wind uplift loads. This paper presents the details and results obtained from this study including suitable design recommendations. It has shown that the recently developed pull-through capacity equations can be used for very thin steel battens. Higher capacity reduction factors are recommended for use with these design equations for battens made of Australian cold-formed steels used in this study. The use of safety lip features did not affect the static pull-through capacities, but it improved the fatigue performance of roof battens. Finally, the suitability of using low strength steel battens instead of high strength steel battens was evaluated.

Fatigue damage models for steel roof battens subject to variable amplitude cyclic wind suction loading

Pull-through failure of steel roof batten to rafter connections is one of the critical failures observed in cold-formed steel roofs during tropical cyclones. Although design equations are available for steel roof battens subject to static pull-through failures, no suitable design equations are available for fatigue pull-through failures. Currently, a Low-High-Low (LHL) cyclic test method based on expensive and time consuming large scale prototype tests is being used to design roof battens for fatigue pull-through failures. Therefore, this research study proposes suitable design equations based on both linear and nonlinear damage models to determine the fatigue life and capacity of steel roof battens by understanding the fatigue behaviour of steel roof battens subject to variable amplitude cyclic wind suction loading. This was achieved through a series of multi-level cyclic tests, including LHL cyclic tests, conducted on roof battens made of different steel grades and thicknesses and fastened with different screw fasteners. This paper presents the details of the experimental study and its results, and proposes suitable fatigue pull-through design equations based on linear and nonlinear fatigue damage models.

Pull-through capacities of cold-formed steel roof battens considering loading rate sensitivity

Static and fatigue pull-through failures of thin steel roof battens in the vicinity of batten to rafter screw connections are part of the major premature connection failures which lead to severe roof failures during high wind events. As wind speed and thereby wind uplift loading rate on a building roof varies over a wide range, the loading rate which should be used to conduct prototype roof tests is a moot point. Current wind loading standards and guidelines recommend a wider range of loading rates/frequencies in simulating static and cyclic wind loads. This could adversely affect the test results of loading/strain rate sensitive materials. Since cold-formed steels appear to be sensitive to loading rate, it is necessary to investigate the effect of loading rate on both static and fatigue pull-through capacities of cold-formed steel roof battens. Therefore, a series of static and cyclic pull-through tests was conducted at various loading rates on roof battens made of two grades (G300 and G550) and two thicknesses (0.75/0.80 and 0.95/1.00 mm). Test results showed that both static and fatigue pull-through capacities increase with increasing loading rate. To understand the loading rate sensitivity of roof battens, the effect of loading rate on the ultimate tensile strength of cold-formed steels was also investigated through a series of tensile coupon tests. Based on both pull-through and tensile coupon test results, suitable modifications and recommendations have been made to the current pull-through capacity equations and the current Low-High-Low (LHL) cyclic test loading frequency. A suitable material model is also proposed to determine the dynamic mechanical properties of cold-formed steels.

Pull-out capacity of multiple screw fastener connections in cold-formed steel roof battens

Light gauge steel roofing systems of low rise buildings are made of high strength steel roof cladding, battens and purlins/rafters/trusses and fastened with self-drilling screws. Localised failures occurring at these screw connections under wind uplift loading often lead to catastrophic losses of steel roofing systems during severe storm events. Pull-out failures occurring at the two bottom flanges of roof batten to purlin/rafter screw connections is one of them. Multiple screw fasteners connecting the bottom flanges of roof battens to purlins/rafters pull out prematurely from the light gauge steel purlins/rafters. Since the structural behaviour of multiple screw connections differs significantly from the behaviour of single screw connections, the pull-out capacity of multiple screw connections cannot be calculated directly based on the number of screw fasteners. Hence a series of 80 small scale pull-out tests was conducted to investigate the pull-out capacities of two and four-screw fastener connections in roof battens. The pull-out failure loads from the tests were first compared with the pull-out capacities predicted using the design equations in the current cold-formed steel design standards. Suitable design modifications were then proposed to accurately calculate the pull-out capacities of roof battens with two and four-screw connections. This paper describes the details and the results of this study.

Development of Suitable Strengthening Methods for Thin Steel Roof Battens Subject to Pull-Through Failures

Failures of the connections of thin-walled steel roof battens to rafters or trusses were increasingly observed in the form of a localized pull-through failure in the batten bottom flanges during recent extreme wind events. Therefore, an extensive research study was conducted to investigate this local connection failure, and suitable test and design methods were developed to accurately determine the design pull-through capacities of roof battens. The study also showed that optimizing the batten geometry is unlikely to increase the pull-through capacity of batten connections to rafters or trusses because they essentially depend on the diameter of the screw fastener head, batten thickness, and steel ultimate tensile strength. Hence, the study was extended to develop suitable strengthening methods to delay or prevent this critical localized connection failure and thus enhance the pull-through capacity. This article first presents the investigations of some current roof construction practices recommended and used by roof batten manufacturers and builders, then proposes the details of suitable strengthening methods. Detailed experimental investigations were undertaken for this purpose, and their results and discussions are presented in this article. In addition, suitable capacity-improvement factors are proposed for the strengthening methods to accurately determine the design pull-through capacities of roof batten connections to rafters or trusses.

Unified static-fatigue pull-through capacity equations for cold-formed steel roof battens

This paper investigates the fatigue pull-through capacity of cold-formed steel roof batten to rafter or truss connections based on static and constant amplitude cyclic tests. In order to represent all steel roof battens used worldwide, test battens were made using 0.75 and 0.95mm G550 and 0.80 and 1.00mm G300 cold-formed steel sheets. Each batten type was tested with 10g and 12g metal self-drilling screws that are commonly used to fasten steel roof battens to rafters or trusses. Tests were conducted using a small scale two-span batten test set-up as recommended by past research studies and simulated wind uplift loading on roof battens. Test results showed that cyclic wind uplift loading significantly reduced the pull-through capacities of steel roof battens, and thereby highlighted the need for accurate fatigue design rules. Therefore, a single-term exponential model was developed to determine the fatigue pull-through capacity reduction factors and was combined with the current static pull-through capacity equations to determine both static and fatigue pull-through capacities of steel roof battens subjected to wind uplift loading. The unified static-fatigue pull-through capacity equations were then verified using further constant amplitude cyclic tests of industrial steel roof battens. The proposed unified equations will facilitate effective designs of cold-formed steel roof battens without conducting the prototype Low-High-Low cyclic tests of roof assemblies.

New test and design methods for steel roof battens subject to fatigue pull-through failures

Thin steel roof claddings and battens are widely used in low rise buildings all around the world. However, they are vulnerable to premature connection failures when subjected to severe wind uplift actions such as those induced by cyclones and storms. Current design methods exclusively depend on full scale prototype roof tests. This paper proposes an alternative design method using a simple equation for thin-walled steel roof battens subjected to fatigue pull-through failures, developed through a series of small scale cyclic wind load tests of roof battens. Since an acceptable small scale connection test method is not available for fatigue pull-through failures of roof battens, various types of small scale connection tests were initially examined to propose the most suitable test method. For this purpose, a series of constant amplitude cyclic tests was conducted using three different small scale test methods (short, cantilever and two-span battens), for a commonly used steel roof batten. Test results showed that the present state of knowledge based on static pull-through studies could lead to the use of a wrong test method in fatigue pull-through studies. This paper has used the cyclic test results from the selected small scale test method to propose a fatigue pull-through design equation. The use of the proposed design equation will lead to conservative outcomes for roof battens and will enable safe roof batten design without the need for full scale cyclic tests of prototype roof assemblies.

07.05: Fatigue life assessment of cold‐formed steel roof battens

ABSTRACTMetal roofs of low‐rise buildings are exposed to highly fluctuating and prolonged suction wind uplift pressures during cyclones. The high suction pressures on roofs lead to premature, low cycle fatigue failures of roof members. Steel roof batten made of thin, high strength cold‐formed steel (CFS) is one of the vulnerable roof members that fails prematurely during cyclones. Pull‐through failure in the vicinity of batten to rafter connection is one of its common failure modes. A preliminary study on this topic revealed that the fatigue pull‐through capacity of a commonly used industrial roof batten is 45% of its static pull‐through capacity. Therefore, in order to assess the fatigue capacity and performance of all available CFS roof battens, a series of constant amplitude cyclic tests was conducted on thin‐walled steel roof battens. Critical parameters which influence the pull‐through failure, such as the steel batten grade, thickness and screw fastener diameter, were considered in the test series. S‐N curves were developed for each combination of the selected critical parameters, and the respective fatigue limits were obtained. Test results led to a simple modification to the recently developed static pull‐through capacity equations in order to include the effects of fatigue. They also improved the understanding of the fatigue behaviour of roof battens. In addition, a series of multi‐level cyclic tests was included in this study to investigate the suitability of the currently available Low‐High‐Low (LHL) cyclic test method. This paper presents the details of this study, and the results.

07.23: Effect of loading rate on the pull‐through capacities of cold‐formed steel roof battens

ABSTRACTLocalised connection failure is the main shortcoming of cold‐formed steel roofing systems subjected to high wind suction loads. Pull‐through failure in the vicinity of roof batten to rafter connection is the major connection failure observed during recent high wind events. Both static and fatigue pull‐through failures occur based on the type of wind loads (static or cyclic loads). The loading rate to be used in the static and cyclic pull‐through failure tests is a moot point as the wind loading frequency can vary during wind events such as storms and cyclones. Therefore, it is necessary to understand the effect of wind loading frequency/rate on the pull‐through failures of steel roof battens. This paper investigates the influence of loading rate on both static and fatigue pull‐through capacities of steel roof battens by means of a series of static and cyclic tests conducted at various loading rates/frequencies. Initially, tests were conducted on roof battens made of two steel grades (G300 and G550) and two thicknesses (0.8 and 1 mm). The results showed a significant improvement in the pull‐through capacities during tests using higher loading rates. They also showed that the current static and cyclic pull‐through design rules/guidelines do not include the effect of loading rate. Secondly, to understand the influence of loading rate on the pull‐through capacity of battens, the effect of loading rate on the mechanical properties of steels was investigated using 40 tensile coupon tests. The effect of loading rate on both the tensile strength of steel used and the pull‐through capacity of roof batten was then compared. Using the results of comparison, the reasons for the increase in the static pull‐through capacity of roof battens with loading rate are discussed and, a recommendation is made in relation to the loading rate to be used with the new Low High Low (LHL) cyclic test. This paper presents the details and results of this study.

Numerical studies and design of thin steel roof battens subject to pull-through failures

High wind uplift loads acting on the light gauge steel roofing systems during tropical cyclones and storms frequently cause premature failures of roof connections, which lead to extensive damage to roofing systems. Such roofing system damage was observed in recent cyclones due to premature failures of steel roof batten to rafter/truss connections. They were mostly observed to be due to a localised pull-through failure in the bottom flanges of roof battens. Hence a series of small scale and full scale tests of roof battens was first conducted to study their pull-through failures. To further enhance the understanding gained from the experimental study and to predict the pull-through capacities of a wide range of roof battens, finite element models were developed and analysed using a suitable failure criterion. This paper first presents the applicability of the failure criterion for different roof batten geometries and screw fastener head sizes. Then it provides the details of a numerical parametric study conducted to study the pull-through failures of roof battens in relation to influential parameters such as batten geometry and screw fastener head sizes. Finally, this paper proposes suitable design equations and capacity reduction factors for the calculation of the design pull-through capacities of thin-walled steel roof battens.

Development of fragility curves for localised pull-through failures of thin steel roof battens

Recent extreme wind events such as tropical cyclones and severe storms have shown that thin steel roof battens fail prematurely at their screw connections to the rafters or trusses. The screw heads connecting the bottom flanges of thin steel roof battens to the rafters or trusses often pull through the roof batten bottom flanges. Since such localised pull-through failures occur in the lower level of roof connections, they often cause the loss of the entire roofing system during extreme wind events. Therefore detailed experimental and numerical studies were conducted at the Queensland University of Technology, and suitable test, design and strengthening methods were developed to accurately design the roof batten to rafter/truss connections and to enhance the roof batten performances under wind uplift loads. However, the levels of possible damages at community level due to the pull-through failures of roof battens are still unknown. Therefore fragility curves were developed in this study to determine the likely level of roof damage during extreme wind events, based on the governing pull-through failures of thin steel roof battens. Detailed probabilistic analyses and Monte Carlo simulations were conducted for this purpose. Fragility curves were also used to evaluate the effects of roof batten span and spacing and, levels of enhancement that could be achieved with the strengthening method proposed for roof battens. This paper presents the details of this study on the development of fragility curves and the results.

Development of Suitable Test Methods for the Screw Connections in Cold-Formed Steel Roof Battens

AbstractThe roofing systems of low-rise buildings are commonly made of thin, high-strength steel roof sheeting and battens. These light-gauge steel roofing systems are subjected to high-wind uplift loads during tropical cyclones and thunderstorms. In recent times, roof batten–to–rafter or truss connection failures have been identified as a major cause of severe roof failures during high-wind events. Most of these connection failures are in the form of localized pull-through failures of the bottom flanges of steel roof battens at their screw connections. The design practice at present is based on expensive and time-consuming full-scale tests or inappropriate small-scale tests. Hence, there is an urgent need to develop suitable test methods to determine the pull-through capacity of roof battens. This paper presents the details of an experimental study undertaken to investigate pull-through failures of light-gauge steel roof battens using both full-scale and small-scale tests. The investigation showed that t...