Franc Sinur

Assessment of the Seismic Response of Concentrically-Braced Steel Frames

The BRACED project investigated the ultimate behaviour of concentrically braced frames (CBFs). The research programme was designed to validate empirical models for the ductility capacity of hollow section bracing members and recent proposals for the improved detailing of gusset plate connections, to identify active yield mechanisms and failure modes in different brace member/connection configurations, and to provide essential data on the earthquake response of European CBFs. The central element of the integrated experimental and numerical research programme is a series of shake table experiments on full-scale model single-storey CBFs designed to Eurocode 8 (CEN EN 1998-1:2004, Eurocode 8: Design of structures for earthquake resistance—Part 1: General rules, seismic actions and rules for buildings. European committee for standardization, 2004). Twelve separate experiments were performed on the Azalee seismic testing facility at CEA Saclay. The properties of the brace members and gusset plate connections were varied between experiments to examine a range of feasible properties and to investigate the influence of conventional and improved design details on frame response. Each experiment examined the response of the test frame and brace-gusset plate specimens to table excitations scaled to produce elastic response, brace buckling/yielding and brace fracture. These experiments were supported by complementary quasi-static cyclic tests and correlative numerical simulations using pushover and time-history analysis using the OpenSees seismic analysis software. The outputs of the research programme represent a unique set of data on the ultimate earthquake response of CBFs with realistic brace members and connections. The principal experimental outcomes include measurements of elastic frame stiffness and its evolution with brace damage, measurements of the displacement ductility capacity of the brace specimens; an evaluation of the influence of brace connection configuration and gusset plate detailing on frame stiffness, damping and ductility; and observations on the contributions of brace and connection yielding to overall inelastic deformation of CBFs.

Longitudinally Stiffened Girders Subjected to Bending Moment

The paper deals with the resistance of plated girders subjected to normal stresses due to bending moment. The elastic critical plate-like buckling stress calculated according to simplified analytical method from EN 1993-1-5 was compared against elastic critical stress calculated with EBPlate software which was further on used to determine bending resistance. This was determined by four proposed methods those were compared against numerical simulations. Finally, the results of numerical analysis were used to statistically evaluate all resistance models and to determine partial safety factors.

BENDING-SHEAR INTERACTION OF LONGITUDINALLY STIFFENED GIRDERS

To understand behaviour of longitudinally stiffened plated girders subjected to high bending moments and shear forces, four tests on large scale test specimens were performed. The results of these tests were used to verify the numerical model, which was employed for further parametric studies. With a verified simplified numerical model a parametric nonlinear analysis was systematically carried out to determine the resistance of longitudinally stiffened plated girders. Based on 630 numerical simulations a new equation for interaction at high bending moments and shear forces is proposed, as is the section, where the check should be performed. An extensive reliability analysis of five different design models was made, i.e., the EN 1993-1-5 interaction model, the proposed new model, the gross cross-section bending resistance model and two models, which are a combination of the first three.

Reliability analysis of net cross-section resistance with accidental eccentricity of holes

The aim of the research was to determine reliability function of net cross-section resistance in relation to accidental eccentricity of nominally centric holes. The response surface method was used by taking into account the relevant Eurocode design provisions and reliability requirements. Within the response surface method, the central composite design method and the least square method were used with the employment of Monte Carlo simulations. The probable distributed variables such as strength fy, breadth b, thickness t, diameter d0 and eccentricity e were determined by the central composite design method. 280 different numerical simulations were set up with varying variables. A log-normal distribution for strength (fy) and a normal distribution for geometrical variables (b, t, d0,e) were employed by taking into account the coefficients of variations: Vfy=0.07, Vb,=0.005, Vl=0.05 and Vd0=0.005. In order to determine the influence of eccentricity on partial safety factor, several normal distributions with different variation factors were applied in the analysis. The influence of the edge distance of the hole e2 over d0 ratio on the partial safety factor was determined by varying mean values of variable b. For comparison, two types of steel were used: structural steel S235 and high strength steel S690. Numerical simulations of the net cross-section resistance Fu were performed with ABAQUS 6.7. The response surface for the net cross-section resistance was determined by introducing a quadratic approximation function and by applying the least square method. The partial safely factor was then (statistically) obtained by means of robust Monte Carlo simulations on the calculated response surface.