Experimental Study on the in-plane behavior of standing seam roof assembly and its use in lateral bracing of rafters

Final Test ReportThe standing seam roof (SSR) system is the most commonly used roof system for metal buildings due to its superior durability, water tightness, and energy efficiency. In this type of system, SSR panels attach to Z-shaped or C-shaped purlins with clips, and the purlins are in turn connected to rafters (i.e. roof beams). For the design of the rafters against lateral torsional buckling, bottom flange braces provide torsional bracing to the rafter and the SSR system provides some lateral bracing. However, the degree to which the SSR system can restrain the rafter against lateral movement has not previously been studied. The objective of this study is to quantify the in-plane strength and stiffness of the SSR system and identify how this can be used to provide lateral bracing to the rafter. A total of 11 full-scale standing seam roof specimens were tested to investigate the effects of different standing seam roof configurations (SSR panel type, clip type, thermal insulation, and purlin spacing) on the in-plane stiffness and strength of the SSR system. The resulting stiffness and peak strength of the specimens were tabulated and compared for different SSR configurations. Results showed that the in-plane load-deformation behavior of SSR systems was governed by clip deformations and that variations in the type of SSR panel or clip can have a major impact on the strength and stiffness of the specimens. A specimen with vertical rib panels was shown to have 16 times more stiffness than a similar specimen with trapezoidal rib panels because the vertical ribs restrain the clip deformation. However, even a small standoff was found to reduce the stiffness of vertical rib SSR assemblies with more than three-fold drop in stiffness as the standoff was increased from 0 in. to 0.4 in. Trapezoidal rib SSR assemblies had consistent strength stiffness with fixed clips having standoff of 0 in. or 0.5 in., but with floating clips the stiffness decreased with increasing standoff. Addition of blanket insulation and thermal blocks were found to result in 60% to 350% increase in stiffness. A method for using these experimental results in calculations of required bracing for metal building rafters is described. An example is also provided which demonstrates that the SSR roof can contribute to bracing of the rafter and may reduce spacing or size of discrete/point torsional braces.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Stiffness of Concrete-Filled Steel Deck Diaphragms

In structural analysis of building structures, the in-plane stiffness diaphragms is needed so that lateral loads will be properly distributed to elements of the lateral-force resisting system. In US building codes, diaphragm stiffness is used to determine whether a diaphragm can be assumed rigid or flexible and is also used in semi-rigid diaphragm analysis. For concrete-filled steel deck diaphragms, methods provided in AISI S310 (AISI, 2020) to calculate stiffness have relied on empirical formulas while past research by Porter and Easterling (1988) suggests that mechanical models and theoretical formulas can accurately capture stiffness. Recently, eight cantilever diaphragm specimens were tested with variations in depth of concrete cover, deck depth, perimeter stud anchor configuration, concrete type (normal weight (NW) and lightweight (LW)), and the presence of either welded wire mesh or reinforcing steel. This report summarizes the results of this testing program as they relate to initial stiffness. The initial stiffness results of this testing program are used in conjunction with the results of a testing program performed Porter and Easterling (1988) to form a set of 25 specimens that are then used to validate a proposed prediction model for the initial stiffness of concrete-filled steel deck diaphragms. The proposed prediction model is based on a theoretical framework proposed by Porter and Easterling (1988) which concluded that the initial stiffness of a concrete-filled steel deck diaphragm is a combination of 1) the diaphragm shear stiffness, 2) the bending stiffness of the concrete-filled steel deck diaphragm combined with the chords, and 3) the stiffness of the shear transfer connections between the concrete-filled steel deck diaphragm and the supporting steel frame. The proposed stiffness predictions using this approach resulted in an average ratio of predicted stiffness to measured stiffness equal to 0.95 with a standard deviation of 0.21. Based on this comparison for 25 cantilever diaphragm specimens, it was deemed that the prediction model accurately represents the initial shear stiffness of concrete-filled steel deck diaphragms. This report also includes two examples to illustrate of how the proposed prediction model can be used to calculate diaphragm deflections for two different diaphragm configurations. The results of these examples showed that for the cantilever diaphragm configuration, the deflection of the free end is mostly due to the shear deformation of the concrete-filled steel deck diaphragm or to the deformation of the shear transfer connection, depending on the spacing of headed stud anchors, with the bending deformations contributing the least to the total deflection. For the case of a simply supported diaphragm, the mid-span deflection was attributed primarily to bending deformations of the diaphragm (78% of total deflection), with shear deformations contributing to approximately 25% of the total deflection and the deformation of the shear transfer connections contributing less than 1% of the total deflection.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Development of Steel Deck Diaphragm Seismic Design Provisions for ASCE 41/AISC 342

The objective of this report is to provide the background work for the development of recommended seismic design provisions for steel deck diaphragms utilizing ASCE 41 / AISC 342. The current (2017) edition of ASCE 41 for the seismic evaluation and retrofit of existing buildings essentially requires that steel deck diaphragms be designed as elastic elements. This potentially results in large economic and design inefficiencies. Recently existing data has been gathered on the cyclic performance of steel deck diaphragms and this data indicates that appreciable ductility can exist in these systems. Following protocols established in ASCE 41 this document uses existing data to develop acceptance criteria and modeling protocols for seismic performance-based design supported by linear or nonlinear analysis. The method requires fitting a multi-linear model to the cyclic backbone response of available data – and parametrically characterizing the fit to the extent possible. It is found that with minor changes the provisions of AISI S310 may be used to establish strength and stiffness and the available test data to determine ductility and post-peak response. Differences between ductility of diaphragms in buildings and diaphragms in sub-assembly tests are noted and recommendations made to handle this difference. Specific new provisions, ready for adoption by AISC 342 / ASCE 41 are recommended for bare steel deck diaphragms and steel deck diaphragms with concrete fill. A list of future challenges, including the need for additional cyclic testing on steel deck diaphragms with concrete fill, are provided.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

SDII Building Archetype Design v2.0

Building designs, SAP models, spreadsheets, and slide decks in support of SDII building archetype designs.Building archetypes are fundamental to exploring and demonstrating the seismic behavior of modern structures. No suitable archetypes or prototypes exist in the open literature that focus on steel deck diaphragms for conventional steel buildings. Three dimensional building analysis, with meaningful contributions from the diaphragm in terms of behavior, has not formed the basis for modern seismic standards in steel at this time. The objectives for the SDII building archetypes include the following. Develop a series of 3D steel-framed archetype buildings that explore and document the design of horizontal lateral force resisting systems (LFRSs) with steel deck-based diaphragms as well as vertical LFRSs and the inter-relationship between the two. Provide a series of buildings that form a common basis of comparison for diaphragms in steel-framed buildings much the same way the SAC buildings did for the vertical LFRS. Explicitly explore the impact of the ASCE 7-16 standard, and ASCE 7-16 alternate diaphragm design with: Rs=1, Rs=2 for steel deck with fill and 2.5 for bare steel deck, and Rs=3 in designs. Inform areas for needed experimentation, and create targets for advancing nonlinear analysis within the full SDII effort.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Seismic Behavior of Steel SCBF Buildings Including Consideration of Diaphragm Inelasticity

SDII ReportThis report provides a summary of nonlinear response history analyses conducted on a three- dimensional model of a series of steel buildings with special concentric braced frames (SCBFs). The models are conducted in OpenSees and include appropriate nonlinear response for the braced frames as well as the concrete-filled steel deck diaphragms and bare steel deck roofs. Additionally the buildings are designed considering traditional diaphragm design as defined by ASCE 7-16 12.10.1 as well as the new alternative diaphragm design procedures of ASCE 7-16 12.10.3. These alternative procedures have a seismic response modification coefficient, Rs, which is specific to the diaphragm system. Rs values between 1 and 3 are investigated herein. The results indicate that SCBF building performance is sensitive to the diaphragm design, and that traditional diaphragm design does not lead to acceptable levels of performance. Use of the alternative diaphragm design procedure with Rs=2.0 for concrete-filled steel deck floors and Rs=2.5 for bare steel deck roofs is recommended. Future work is needed to continue to refine collapse criteria for 3D building models and to allow the engineer greater clarity in the extent of expected inelasticity in the vertical system vs. the diaphragm system when different combinations of R and Rs, i.e. different combinations of vertical and horizontal lateral force resisting systems, are employed.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Cantilever Testing of Concrete-Filled Steel Deck Composite Diaphragms Using Various Types of Steel Reinforcing

This report provides a summary of nonlinear response history analyses conducted on a three- dimensional model of a series of steel buildings with special concentric braced frames (SCBFs). The models are conducted in OpenSees and include appropriate nonlinear response for the braced frames as well as the concrete-filled steel deck diaphragms and bare steel deck roofs. Additionally the buildings are designed considering traditional diaphragm design as defined by ASCE 7-16 12.10.1 as well as the new alternative diaphragm design procedures of ASCE 7-16 12.10.3. These alternative procedures have a seismic response modification coefficient, Rs, which is specific to the diaphragm system. Rs values between 1 and 3 are investigated herein. The results indicate that SCBF building performance is sensitive to the diaphragm design, and that traditional diaphragm design does not lead to acceptable levels of performance. Use of the alternative diaphragm design procedure with Rs=2.0 for concrete-filled steel deck floors and Rs=2.5 for bare steel deck roofs is recommended. Future work is needed to continue to refine collapse criteria for 3D building models and to allow the engineer greater clarity in the extent of expected inelasticity in the vertical system vs. the diaphragm system when different combinations of R and Rs, i.e. different combinations of vertical and horizontal lateral force resisting systems, are employed.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Development of Steel Deck Diaphragm Seismic Design Provisions for ASCE 41/AISC 342

The objective of this report is to provide the background work for the development of recommended seismic design provisions for steel deck diaphragms utilizing ASCE 41 / AISC 342. The current (2017) edition of ASCE 41 for the seismic evaluation and retrofit of existing buildings essentially requires that steel deck diaphragms be designed as elastic elements. This potentially results in large economic and design inefficiencies. Recently existing data has been gathered on the cyclic performance of steel deck diaphragms and this data indicates that appreciable ductility can exist in these systems. Following protocols established in ASCE 41 this document uses existing data to develop acceptance criteria and modeling protocols for seismic performance-based design supported by linear or nonlinear analysis. The method requires fitting a multi-linear model to the cyclic backbone response of available data – and parametrically characterizing the fit to the extent possible. It is found that with minor changes the provisions of AISI S310 may be used to establish strength and stiffness and the available test data to determine ductility and post-peak response. Differences between ductility of diaphragms in buildings and diaphragms in sub-assembly tests are noted and recommendations made to handle this difference. Specific new provisions, ready for adoption by AISC 342 / ASCE 41 are recommended for bare steel deck diaphragms and steel deck diaphragms with concrete fill. A list of future challenges, including the need for additional cyclic testing on steel deck diaphragms with concrete fill, are provided.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Experimental Study on the in-plane behavior of standing seam roof assembly and its use in lateral bracing of rafters

Final Test ReportThe standing seam roof (SSR) system is the most commonly used roof system for metal buildings due to its superior durability, water tightness, and energy efficiency. In this type of system, SSR panels attach to Z-shaped or C-shaped purlins with clips, and the purlins are in turn connected to rafters (i.e. roof beams). For the design of the rafters against lateral torsional buckling, bottom flange braces provide torsional bracing to the rafter and the SSR system provides some lateral bracing. However, the degree to which the SSR system can restrain the rafter against lateral movement has not previously been studied. The objective of this study is to quantify the in-plane strength and stiffness of the SSR system and identify how this can be used to provide lateral bracing to the rafter. A total of 11 full-scale standing seam roof specimens were tested to investigate the effects of different standing seam roof configurations (SSR panel type, clip type, thermal insulation, and purlin spacing) on the in-plane stiffness and strength of the SSR system. The resulting stiffness and peak strength of the specimens were tabulated and compared for different SSR configurations. Results showed that the in-plane load-deformation behavior of SSR systems was governed by clip deformations and that variations in the type of SSR panel or clip can have a major impact on the strength and stiffness of the specimens. A specimen with vertical rib panels was shown to have 16 times more stiffness than a similar specimen with trapezoidal rib panels because the vertical ribs restrain the clip deformation. However, even a small standoff was found to reduce the stiffness of vertical rib SSR assemblies with more than three-fold drop in stiffness as the standoff was increased from 0 in. to 0.4 in. Trapezoidal rib SSR assemblies had consistent strength stiffness with fixed clips having standoff of 0 in. or 0.5 in., but with floating clips the stiffness decreased with increasing standoff. Addition of blanket insulation and thermal blocks were found to result in 60% to 350% increase in stiffness. A method for using these experimental results in calculations of required bracing for metal building rafters is described. An example is also provided which demonstrates that the SSR roof can contribute to bracing of the rafter and may reduce spacing or size of discrete/point torsional braces.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Semirigid Diaphragm Analysis of Archetype Floor Using Design Office Models

Diaphragms are the floor or roof structures in a building that transfer lateral load horizontally to the braced frames or shear walls. For many types of buildings, the building code requires semirigid diaphragm analysis whereby a three-dimension computer model of a building is created with diaphragm elements that can deform elastically. As a companion to a research project called the Steel Diaphragm Innovation Initiative (SDII), this report describes the semirigid diaphragm analysis of typical floors from archetype buildings. In other publications, the archetype buildings are analyzed using advanced simulation techniques that capture nonlinearity and failure of the diaphragms. The models in this report use software and modelling techniques typical in structural engineering practice and therefore allow the evaluation of design office models for use in understanding behavior of diaphragms during extreme loads such as earthquakes.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF

Semirigid Diaphragm Analysis of Archetype Floor Using Design Office Models

Diaphragms are the floor or roof structures in a building that transfer lateral load horizontally to the braced frames or shear walls. For many types of buildings, the building code requires semirigid diaphragm analysis whereby a three-dimension computer model of a building is created with diaphragm elements that can deform elastically. As a companion to a research project called the Steel Diaphragm Innovation Initiative (SDII), this report describes the semirigid diaphragm analysis of typical floors from archetype buildings. In other publications, the archetype buildings are analyzed using advanced simulation techniques that capture nonlinearity and failure of the diaphragms. The models in this report use software and modelling techniques typical in structural engineering practice and therefore allow the evaluation of design office models for use in understanding behavior of diaphragms during extreme loads such as earthquakes.American Institute of Steel Construction (AISC), American Iron and Steel Institute (AISI), Steel Deck Institute (SDI), Steel Joist Institute (SJI), Metal Building Manufacturers Association (MBMA), National Science Foundation (NSF