Colin A. Rogers

Dynamic Testing of Single- and Double-Story Steel-Sheathed Cold-Formed Steel-Framed Shear Walls

AbstractThis paper describes an experimental investigation of steel-sheathed cold-formed steel-framed shear walls by means of dynamic shake table tests. The objective was to evaluate the seismic performance and to identify whether the shear-wall behavior was consistent with past static tests, to obtain measures of damping and natural period of vibration, to investigate the influence of a second story, and to validate and improve the accuracy of the numerically predicted force-deformation response. The scope of study comprised five single-story and five double-story walls of the platform framing technique. Each wall was subjected to a suite of excitations: impact test to measure the linear-viscous damping ratio, harmonic excitation to estimate the natural period of vibration, and ground motions representative of the seismic hazard in Canada. An overview is presented of the test setup and dynamic loading protocols, as well as the test results and numerical model.

Flange/web distortional buckling of cold-formed steel sections in bending

Abstract Recent experimental tests of cold-formed steel C- and Z-sections in bending have revealed unconservative results in the prediction of the bending moment resistance, using the current North American Design Standards. The failure mode of these tests was identified as flange/web distortional buckling. This mode of failure initially involves a rotation of the lip/flange component about the flange/web corner, which typically occurs for short half-wavelength distortional buckling. Near ultimate failure, an apparent lateral movement of the flange/web corner, which includes transverse bending of the web, is experienced. Various analytical methods that predict the moment resistance of sections which experience short half-wavelength distortional buckling were investigated and compared with the applicable test data. The modified Lau and Hancock 2 Model, with S136-94 Standard calculated effective section modulus, is recommended for use as the North American predictor model for the flange/web distortional buckling moment resistance of cold-formed steel sections in bending.

Bolted connection design for sheet steels less than 1.0 mm thick

Abstract The results of recently completed shear tests indicate that the current connection provisions set out in the AS/NZS 4600, AISI and Eurocode cold formed steel design standards cannot be used to accurately predict the failure mode of bolted connections that are fabricated from thin G550 and G300 sheet steels. Furthermore, these design standards cannot be used to accurately determine the bearing resistance of bolted specimens based on a failure criterion for predicted loads. The measured variation in bearing resistance between thin 0.42 mm G550 sheet steels and typical 1.0 mm and thicker sheet steels has been used to develop a gradated bearing coefficient method, which is dependent on the thickness of the connected materials and the size of the bolt(s) used in the connection. It is recommended that the gradated bearing coefficient formulation, the unreduced net section resistance, and the Eurocode design method for end pull-out be used in the design of bolted connections.

Fracture toughness of G550 sheet steels subjected to tension

Abstract Tension tests of thin G550 sheet steels have shown that coupon specimens, which were obtained from blanks positioned transverse to the rolling direction, fail suddenly soon after yielding has occurred, with minimal plastification of the cross-section. In previous reports the authors have concluded that the ability of G550 sheet steels to undergo deformation is dependent on the direction of load within the material, where transverse specimens exhibit the least amount of overall, local and uniform elongation. Sheet steels of this type do not meet the specified design standard ductility requirements, which are based on the work of Dhalla and Winter (Dhalla AK, Winter G. Steel ductility measurements. J. Struct. Div., ASCE 1974;100(ST2):427–444., Dhalla AK, Winter G. Suggested steel ductility requirements. J. Struct. Div., ASCE 1974;100(ST2):445–462. This paper reports on the fracture resistance properties of G550 sheet steels that are loaded in tension. The Mode I, crack opening, fracture resistance of G550 sheet steels is measured for a range of temperatures and a numerical study of the effect of cracks on structural performance in the elastic deformation range is completed using the results of previously completed tests, as well as the FRANC2D finite element computer program.

ANALYSIS, TESTING AND DESIGN OF STEEL ROOF DECK DIAPHRAGMS FOR DUCTILE EARTHQUAKE RESISTANCE

An experimental program was conducted to study the inelastic response of steel roof deck diaphragms for low-rise steel buildings subjected to seismic loading. Tests were performed on 3.6 m×6.1 m diaphragm specimens made of corrugated steel deck panels. The parameters examined were the thickness and configuration of the sheet steel panels, the type and spacing of the fasteners, the applied loading history and the influence of end lap joints. Diaphragms built with screwed side lap fasteners and nailed deck-to-frame connectors exhibited a pinched hysteretic behaviour, but could sustain large inelastic deformation cycles with limited strength degradation. This type of diaphragm construction could be designed to resist earthquake effects in the inelastic range. Higher shear resistance and less pinching was observed for systems that included welded with washer connections. However, their strength decreased rapidly after the peak load was reached, and hence, these systems should be designed for limited inelastic response. Deck systems with button punched side laps and frame welds without washers showed a brittle response and should be designed to remain elastic under severe earthquake motions. The inelastic demand was found to increase when the spacing of the fasteners was reduced. Specimens constructed with an internal overlap joint exhibited extensive warping of the cross section mainly due to the shorter panel length.

Stability and ductility of thin high strength G550 steel members and connections

Abstract High strength cold-reduced steel is typically of stress grade G550 (550 MPa nominal yield and tensile strength) and less than 1 mm thick. The steel has been used for many years for sheeting and decking but is now being used for structural members such as roof trusses and stud walls of steel framed houses. The paper summarises a major research program on the stability and ductility of this steel which has been proceeding for several years at the University of Sydney. The paper relates the Sydney research to the work of others being undertaken around the world.

Method for the design of light gauge steel frame/wood panel shear walls

Publisher Summary The chapter discusses the method for the design of light-gauge steel frame/wood panel shear walls. An extensive research program of light-gauge steel frame / wood panel shear walls under lateral in-plane loading has led to the development of a recommended design method for use with the 2005 National Building Code of Canada (NBCC). Nominal shear strength and elastic stiffness values are recommended for use with shear walls constructed as per the test specimens. Additional design information including a resistance factor, force modification, and over-strength factors, as well as load duration factors are provided in the chapter. However, tabulated resistances do not account for gravity loading in combination with lateral in-plane loading. This failure mode may control the maximum applied lateral load and could lead to overall structural failures when gravity loads are present. Studies to quantify the effect of gravity loading on shear-wall lateral performance are ongoing. Prior to the proposal of final provisions for a seismic design, analytical studies that incorporate the hysteretic capacity vs. shear displacement relationships of the shear walls are necessary. This includes the nonlinear time-history dynamic analysis of representative structures, designed according to the procedure recommended herein, under selected earthquake records as well as shake table testing.

Shake Table Test of a Half-Scale 2-Storey Steel Building Seismically Retrofitted Using Rocking Braced Frame System

The article introduces a shake table test program that was conducted to investigate the response of a two-storey rocking braced frame for which self-centring capacity is provided solely by the gravity loads supported by the frame. The test specimen is a 0.5 scaled model of a prototype rocking frame that was studied for the retrofit of a seismically deficient steel structure. The main objectives of the test program were to study the effects of column uplift and impact on shear forces and moments in the beams connected to the columns. Higher mode effects on brace forces were also of interest. Three different energy dissipation mechanisms located at the rocking interface were examined for drift control: friction, ring spring dampers, and vertical steel bars yielding in tension and buckling in compression. By changing the seismic weight of the test specimen, tests could be conducted for structures located in two different seismic regions of Canada to study the effect of the signature of the ground motions. Increases in beam forces due to column uplift and impact, as predicted by previous numerical simulations, were confirmed by the tests. High axial loads induced by the second vibration mode were also measured in the second storey braces.

Seismic Performance Characterization of Wood-Sheathed and Cold-Formed Steel Framed Floor and Roof Diaphragm Structures

AbstractThis paper describes a research program involving wood-sheathed and cold-formed steel (CFS) framed diaphragm assemblies. The diaphragm’s response to in-plane monotonic and reversed cyclic l...

Influence of seismic design requirements and building period on the design of low-rise steel buildings

Publisher Summary Single-storey steel buildings are used for light industrial, commercial, and recreational purposes, and represent a vast proportion of the building stock in Canada. The seismic force resisting system (SFRS) of these structures typically includes a steel roof deck diaphragm that transfers horizontal loads to vertical steel bracing bents. The roof diaphragm is made of corrugated steel deck panels that are fastened to each other to support beams and joists. These diaphragms are relatively flexible, and in-plane roof deformations due to lateral loads must be accounted for in a design. In seismically active regions, structures designed according to modem building codes are expected to experience some degree of inelastic response under strong earthquakes. The chapter presents a study to examine the impact of capacity design provisions and period limitations prescribed in Canadian design codes and standard on the cost of low-rise steel buildings. The results show that capacity design provisions significantly influence the cost of the structure, especially when tension-compression bracing is used. Allowing inelastic response in the roof diaphragm can also contribute in reducing the cost of the structure.