The 1st Student Competition on Cold-formed Steel Design

The first Student Competition on Cold-Formed Steel Design (CFS Competition) was held at the University of North Texas in 2011. The CFS Competition was initiated by Cheng Yu through a National Science Foundation CAREER award. The objective of the CFS Competition is to promote higher education in coldformed steel structural design and to encourage students to use creative thinking skills to solve engineering problems. The subject of the first CFS Competition is to design an optimal thin-walled cold-formed steel cross section under several pre-defined restrictions. The CFS Completion received total 78 entries from students in 5 different countries. The judging panel considered the elastic buckling performance, the constructability, and the essay in ranking the designs. This paper presents the details of the competition problem, the results, and findings which are helpful for future competitions

Direct Strength Design of Metal Building Wall and Roof Systems - Through-fastened Simple Span Girts and Purlins with Laterally Unbraced Compression Flanges

A Direct Strength Method (DSM) prediction approach is introduced and validated for metal building wall and roof systems constructed with steel panels through-fastened with screws to girts or purlins. The focus is capacity prediction for simple spans under wind uplift or suction, however the DSM framework is generally formulated to accommodate gravity loads, continuous spans, standing seam roofs, and insulated roof and wall systems in the future. System flexural capacity is calculated with the usual DSM approach – global buckling, local global buckling interaction, and distortional buckling strengths are determined with a finite strip eigen-buckling analysis including a rotational spring that simulates restraint provided by the through-fastened steel panel. The DSM flexural capacity is then reduced with a code-friendly equation consistent with existing Eurocode provisions to account for the additional stress at the intersection of the web and free flange that occurs as the girt or purlin rotates under a suction (uplift) load. A database of 62 simple span tests was assembled to evaluate strength prediction accuracy of the proposed DSM approach alongside existing Eurocode and American Iron and Steel Institute (AISI) provisions. The proposed DSM approach is confirmed to be viable and accurate for simple spans. Modifications to the Eurocode approach are proposed, and if they are made, the Eurocode is also an accurate and potentially general prediction method. The AISI R-factor prediction method is accurate for C-section simple spans, unconservative for Z-section simple spans, and overall lacks the generality of the DSM and Eurocode

Critical Elastic Shear Buckling Stress Hand Solution for C- and Z-sections Including Cross-section Connectivity

This paper presents an approximate solution for the critical elastic buckling stress of cold-formed steel C- and Z-section members including cross-section connectivity. The elastic buckling solution is developed to support the extension of the Direct Strength Method to the shear ultimate limit state, where the cross sectional critical elastic shear buckling stress (load) is employed to predict shear capacity. The shear buckling stress and buckled half-wavelength are calculated with a classical energy solution for a thin plate with edges rotationally restrained. Rotational stiffness expressions in the AISI S100-07 specification, originally derived for distortional buckling of C- and Z-sections, are used with the energy solution to calculate the rotational restraint provided to the web flange juncture by the flanges. The approach is validated with thin shell finite element eigen-buckling analysis

Metal Building Roof Purlin Line Strength by Computation

A computation-based method for metal building purlin and girt design is introduced using the AISI S100-16 North American Specification for the Design of Cold-Formed Steel Structural Members. Purlin section properties, span length, material properties, and boundary conditions, including bracing connectivity to exterior screw-fastened or standing seam panels, are defined. Flexure, shear, and torsional strengths are calculated along the line. The capacity of the roof or wall system is determined by applying a gravity or uplift load until a strength limit state is reached. For uplift loads, buckling deformation of the purlin free flange between intermediate bridging is considered. The calculations are performed with an open-source software package called StructuresKit.jl written in the Julia computing language. Predicted strengths from the calculation method are compared to the experimentally determined strengths from 49 simple span Cee and Zee wall girt line uplift pressure box tests, some of which were constructed with rigid board insulation

Direct Strength Design of Cold-Formed Steel Members with Perforations

Cold-formed steel (CFS) structural members are commonly manufactured with holes to accommodate plumbing, electrical, and heating conduits in the walls and ceilings of buildings. Current design methods available to engineers for predicting the strength of CFS members with holes are prescriptive and limited to specific perforation locations, spacings, and sizes. The Direct Strength Method (DSM), a relatively new design method for CFS members validated for members without holes, predicts the ultimate strength of a general CFS column or beam with the elastic buckling properties of the member cross- section (e.g., plate buckling) and the Euler buckling load (e.g., flexural buckling). This research project, sponsored by the American Iron and Steel Institute, extends the appealing generality of DSM to cold-formed steel beams and columns with perforations.American Iron and Steel Institut

An open-source cold-formed steel connection test database to support future data models

A data structure and physical test database are implemented for cold-formed steel connections. The database is publicly available on GitHub in a format that is both human-readable and machine-readable. The data structure is designed to accommodate connection tests with varying test variables including fastener type, quantity of fasteners in a specimen, and the number and type of plies. The database design is made compatible with open-source software tooling to support future data-driven model development. Strategies are discussed for encouraging general user adoption of open-source databases and software including education, community guidelines, and easy-to-use interfaces

Evaluation of Metal Building System Seismic Response Modification Coefficients

NBM ReportA seismic evaluation was conducted of common metal building configurations within the probabilistic framework defined in FEMA P695 “Quantification of Building Seismic Performance Parameters” with the goal of evaluating the applicability of current seismic design procedures in the ASCE 7-10 “Minimum Design Loads for Buildings and Other Structures”. The evaluation began with the definition of a performance group of index archetypes which was guided by industry steering group-led design studies that explored the influence of seismic load combinations and geographical location on the primary frame design. It was observed that taller, shorter span buildings in the western U.S. were most sensitive to seismic demands. This led to the definition of a performance group covering a range of natural periods and seismic weights designed to ASCE Seismic Category D and with the seismic response modification factor of ​R​=3.5. The seismic parameters calculated for the performance group, designed by industry with ASCE Equivalent Lateral Force procedures, were the system overstrength, ductility, and probability of system collapse when exposed to the Maximum Considered Earthquake (MCE) which has a 2% probability of exceedance in 50 years. The system overstrength and ductility for each index archetype were calculated with simulated experiments using thin shell high fidelity simulation, where all metal building components were modeled including the built-up primary frames, the girts and purlins, the exterior metal facade and screw down roof, the rod bracing, and the primary frame flange braces that are important for controlling lateral-torsional buckling. The high fidelity simulation protocol was extensively validated with research between 2006 and 2013 that included monotonic and cyclic primary frame subassembly tests and shake table tests at the University of California, San Diego. The simulated pushover experiments revealed significant system overstrength in the index archetypes and a post-peak ductile response that was sensitive to the controlling limit state. When primary frame lateral-torsional buckling was controlled by the intermediate flange braces, post-peak deformation was available out to large drifts. Panel zone buckling at the knee of the column/rafter resulted in steady post-peak strength degradation. The heavy wall buildings had a higher pushover strength than the light wall buildings because the seismic design load combinations were more influential on the heavy wall primary frame design. The same high fidelity models were used to characterize the quasi-static cyclic response for each index archetype using an accepted American Institute for Steel Construction (AISC) industry loading protocol. The cyclic response, including strength and stiffness degradation from local and global buckling and column-rafter knee panel zone tension field yielding, was fit to a nonlinear Single-Degree-of Freedom (SDOF) material model used for incremental dynamic analysis (IDA). The IDA performances from 44 far-field ground motions required by FEMA P695 led to a cumulative distribution function of spectral intensity of the far-field record set which could be used to calculate the median collapse probability for each index archetype. 4 Uncontrolled collapse was never observed for these light buildings in the simulations or the shake table experiments, however fracture was, in the knee-rafter panel zone from shear buckling and in the rafter taper joints after lateral-torsional buckling. Both drift and fracture studies were conducted to settle on a drift-based collapse limit of 4.5% for the performance group. The collapse margin ratio, defined as the spectral acceleration at median collapse probability to the spectral acceleration from the Maximum Considered Earthquake (MCE) was on average across the metal building performance group higher than the acceptable collapse margin ratio corresponding to a 10% collapse probability, with no outliers greater than 20%. This confirms the viability of the existing ASCE 7 equivalent lateral force seismic design procedures for metal buildings in the performance group considered. With the seismic evaluation process now established and validated, the metal building industry can now investigate other performance groups with potentially large commercial impact - for example, heavier roof buildings that are outside the limits of current ASCE 7 procedures. A modular metal building seismic performance group also becomes available for study with the verified high fidelity modeling protocol used to perform simulated pushover experiments and to quantify cyclic performance.Metal Building Manufacturers Associatio

Structural Analysis in Virtual Reality for Education with BMLY

Virtual reality (VR) is an engaging and immersive medium for interacting with a digital environment. The educational benefits of implementing virtual reality into learning modules has recently been explored. This work presents a process for creating a virtual reality learning module on beam bending and a preliminary study on its effectiveness. In this work, virtual reality and structural analysis are combined to create an interactive virtual experiment on a steel beam. A VR user can select the location of a gravity load along the member and increase its magnitude while following the deformation and stresses in real time. The VR environment is implemented using the open source three.js library. The results of a survey to assess student interaction and evaluation of the developed learning module is presented.The authors would like to acknowledge the support of The University of Sydney for the time in the Immersive Learning Laboratory which facilitated this work

Life Cycle Assessment of Tall Buildings in Qatar, A focus on Construction Materials Use and Techniques

Buildings represent one of the most significant sources of negative impacts to the natural ecosystems on which Qatar's inhabitants health and environmental quality depend. The market has identified Qatar as one of the busiest construction areas in the world (Ibrahim 2011), While rapid economic development, population growth, and construction boom are positive indicators of growth, they may also present issues related to the negative impact on the socio-environmental components of cities. Such is the case of the Gulf Cooperation Council (GCC) countries where increasing economic prosperity has led to a surge in tall building construction and a sense of competition to erect the tallest skyscrapers in the world (Mahgoub and Abarra 2012). While tall buildings are a source of national pride and cultural identity enabled by economic prosperity, they pose several challenges to integrate with the urban fabric of the city while also having a tremendous environmental impact. Tall buildings are especially massive consumers of energy (Ali and Armstrong 2008). They are the dominant elements in urban architecture due to their scale and purpose, and should be the focus of sustainable design. With large number of towers constructed and to be constructed in Al Dafna and West Bay areas of Doha, these buildings affect different aspects of the built and urban environment, i.e., city image, traffic, urban spaces and physical conform. Therefore, more architectural design strategies have to be planned well ahead in order to tackle the issues of sustainability and adaptability to climate change and to foster sustainable built environment in the state of Qatar. With Qatar slated to host a 'zero carbon' World Cup in 2022, Qatar Green Building Council (QGBC) has set up a group to foster green infrastructure as a national resource. Qatar is utilizing Leadership in Energy and Environmental Design (LEED) and the Global/Qatar Sustainability Assessment System (GSAS/QSAS) to this end. Furthermore, shortages in raw materials between 2013 and 2017 are expected to challenge the construction sector, as the period is expected to be the peak for the sector. Therefore, the sector will have to bridge the gap during this period by mutual agreements with the companies in Saudi Arabia and the UAE (QCB 2012). The objectives of this paper are as follows: 1- to Identify sustainability metrics for tall buildings with focus on construction materials and methods used in Qatar; 2- Explore existing literature and identify analogies in optimization consistent with design variables; 3- to examine sustainability of construction materials used in Qatar by utilizing software which is based on currently available databases to perform life cycle assessment. To meet the objectivess described above, the currently available software platforms to perform life cycle analysis of building materials were explored. A commercial software, SimaPro, which utilizes the environmental impact database Ecoinvent, was chosen for its flexibility in defining custom mix designs for concrete, as well as database information on steel and many other building materials. With SimaPro, a sustainability model for concrete and steel was developed which reflects the environmental implications of manufacture of materials in Qatar as appropriate. Quantitative results from the model for the sustainability of constituents of building materials were extracted, to form the basis of sustainability metrics in the forthcoming tall building topology optimization protocol. Furthermore, Blanco-Carrasco et al (2010) outline reduced use of Portland cement, increased use of alternate cementitious materials, and reduced water use to improve the sustainability of the concrete industry in Qatar. Using structural models and the SimaPro model, ultra-high performance concrete was explored as a potential solution for all these problems, to be applied in the gravity/lateral structural components of Qatar tall buildings. In addition to identifying a novel material which fits well with the current tall building designs of the region, the process of examining the structural and environmental improvements from using ultra-high performance concrete has resulted in the formation of a procedure to compare multiple materials used in Qatar.qscienc

Direct Strength Design of Cold-Formed Steel Members with Perforations

Cold-formed steel (CFS) structural members are commonly manufactured with holes to accommodate plumbing, electrical, and heating conduits in the walls and ceilings of buildings. Current design methods available to engineers for predicting the strength of CFS members with holes are prescriptive and limited to specific perforation locations, spacings, and sizes. The Direct Strength Method (DSM), a relatively new design method for CFS members validated for members without holes, predicts the ultimate strength of a general CFS column or beam with the elastic buckling properties of the member cross- section (e.g., plate buckling) and the Euler buckling load (e.g., flexural buckling). This research project, sponsored by the American Iron and Steel Institute, extends the appealing generality of DSM to cold-formed steel beams and columns with perforations.American Iron and Steel Institut