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

Characterizing the Load Deformation Behaviour of Steel Deck Diaphragms

Lateral loads flow through a building’s horizontal roof and floor diaphragms before being transferred to the vertical lateral force resisting system (e.g. braced frames, moment frames or shear walls). These diaphragms are therefore a critical structural component in the resistance of lateral loads. A review of the literature shows that a large number of experimental programs have been performed to obtain the in-plane load-deformation behavior of steel deck and concrete on steel deck diaphragms. The tested diaphragm behavior was found to be dependent on a set of factors including loading protocol, fastener type, fastener size and spacing, and more. There does not currently exist a single, unifying review of these diaphragm tests and their relevant results. A research program is being conducted to collect and consolidate the available literature about tested steel deck diaphragms and their results. A database has been created that includes over 450 tested specimens with more than 130 cyclic tests. In addition, an effort is made to characterize diaphragms’ load-deformation response as grouped by sidelap and support fastener type. The test programs and results collected into this database as well as the characterization of diaphragm behavior are discussed in this paper

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

Compression-tension Hysteretic Response of Cold-formed Steel C-stection Framing Members

This paper summarizes results from an experimental program designed to evaluate the tension-compression cyclic axial response of cold-formed steel C-section structural framing members. A new cyclic loading protocol for cold formed steel members is presented that defines the target axial displacement based on elastic buckling parameters. The protocol is used to explore the cyclic response of members experiencing local buckling, distortional buckling, and global buckling deformation. In the experiments, post-bucking energy dissipation was observed along with tension stretching and softening. The quantity of dissipated energy per cycle increased as cross-section and global slenderness decreased. Specimens experiencing local and distortional buckling dissipated more energy per half-wavelength than those experiencing global buckling

Local Buckling Hysteretic Nonlinear Models for Cold-Formed Steel Axial Members

This paper studies the energy dissipation and damage in thin walled members that experience local buckling and presents an approach to model cold-formed steel (CFS) axial members that experience local buckling deformations. The model is implemented in OpenSees using hysteretic models for CFS axial members calibrated using experimental responses. Results from thin-shell element simulations using ABAQUS show that energy dissipation in thin plates dissipates through inelastic strains and yielding that concentrates in damaged zones that extent approximately the length of a buckled half-wave (Lcr). Generally damage accumulates in one zone but when more than one damaged zone occurred the energy dissipation increased proportionally. The results from the plate simulation and experimental results from cyclic tests on axially loaded CFS members (previously performed by the authors) support the assumptions for the modeling approach presented for CFS members governed by local buckling. Results demonstrate the capabilities of the modeling approach to efficiently and accurately simulate the response of the CFS axial members experiencing local buckling. The model presented can be used to facilitate the performance assessment of cold-formed steel lateral load resisting systems (e.g., shear walls) under different hazard/performance levels, a capability needed for the advance of performance-based earthquake engineering of cold-formed steel buildings

Analysis of Fracture Behavior of Large Steel Beam-Column Connections

[EN] Recently completed experimental steel beam-column connection tests on the largest specimens of reduced-beam section specimens ever tested have shown that such connections can meet current seismic design qualification protocols, allowing to further extend the current AISC Seismic Provisions and the AISC Provisions for Prequalified Connections for Special and Intermediate Steel Moment Frames. However, the results indicate that geometrical and material effects need to be carefully considered when designing welded connections between very heavy shapes. Understanding of this behavior will ease the use of heavier structural shapes in seismic active areas of the United States, extending the use of heavy steel sections beyond their current use in ultra-tall buildings. To better interpret the experimental test results, extensive detailed finite element analyses are being conducted on the entire series of tests, which comprised four specimens with beams of four very different sizes. The analyses intend to clarify what scale effects, at both the material and geometric level, influence the performance of these connections. The emphasis is on modeling of the connection to understand the balance in deformation between the column panel zones and the reduced beam section, the stress concentrations near the welds, the effects of initial imperfections and residual stresses and the validity of several damage accumulation models. The models developed so far for all four specimens have been able to accurately reproduce the overall load-deformation and moment-rotation time histories.These studies were made possible by a grant from the National Scholarship Council of China to Mr. Qi and by the generosity of the Advanced Research Computing Center at Virginia Tech.Qi, L.; Paquette, J.; Eatherton, M.; Leon, R.; Bogdan, T.; Popa, N.; Nunez, E. (2018). Analysis of Fracture Behavior of Large Steel Beam-Column Connections. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 521-526. https://doi.org/10.4995/ASCCS2018.2018.7122OCS52152

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

Characterizing the load-deformation behavior of steel deck diaphragms using past test data

Recent research has identified that current code level seismic demands used for diaphragm design are considerably lower than demands in real structures during a seismic event. However, historical data has shown that steel deck diaphragms, common to steel framed buildings, perform exceptionally well during earthquake events. A new alternative diaphragm design procedure in ASCE 7-16 increases diaphragm seismic demand to better represent expected demands. The resulting elastic design forces from this method are reduced by a diaphragm design force reduction factor, Rs, to account for the ductility of the diaphragm system. Currently, there exist no provisions for Rs factors for steel deck diaphragms. This research was therefore initiated to understand inelastic steel deck diaphragm behavior and calculate Rs factors. A review of the literature showed that a large number of experimental programs have been performed to obtain the in-plane load-deformation behavior of steel deck diaphragms. To unify review of these diaphragm tests and their relevant results, a database of over 750 tested specimens was created. A subset of 108 specimens with post-peak, inelastic behavior was identified for the characterization of diaphragm behavior and ductility. A new recommended method for predicting shear strength and stiffness for steel deck diaphragms with structural concrete fill is proposed along with an appropriate resistance factor. Diaphragm system level ductility and overstrength are estimated based on subassemblage test results and Rs factors are then calculated based on these parameters. The effects of certain variables such as deck thickness and fastener spacing on diaphragm ductility are explored.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