Dat Duthinh

Wind Effects on Low-Rise Metal Buildings: Database-Assisted Design versus ASCE 7-05 Standard Estimates

Peak bending moments are compared for a set of steel portal frames of industrial buildings in an open terrain calculated using database-assisted design (DAD) techniques and ASCE 7-05 Standard plots. The comparisons indicate that, depending on the building dimensions, the peak bending moments at the knee based on DAD techniques are generally larger by 10–30% than their counterparts based on the ASCE 7-05 plots. (In one case with a relatively steep roof slope of 26.6° the discrepancies exceed 70%.) For the buildings considered, the discrepancies increase with increasing roof slope and with increasing eave height.

Risk Consistency and Synergy in Multihazard Design

Current design procedures in the United States use the envelope of individual hazard demands on a structure to ensure safety against multiple hazards. A difficulty in multihazard design for wind and earthquake is that the load and resistance factor method makes use of different design philosophies developed by different subdisciplines. Seismic design explicitly allows for inelastic behavior. In contrast, wind design assumes that, before application of a resistance factor less than unity, the limit state is defined by the development of the first plastic hinge in a structural member. This paper focuses on the issue of risk consistency in multihazard design, and shows that, in spite of this difficulty, it is possible to quantify the risks of arriving at a particular lateral drift state for structures exposed to multiple nonsimultaneous hazards and to compare them to the risks for the same structures subjected to a single hazard. A second focus is the issue of multihazard design synergy. It has been pointed ...

Instability of steel gusset plates in compression

As a result of the structural failure of the I-35W Bridge in Minneapolis in 2007, the Federal Highway Administration (FHWA) issued guidelines for the load rating of gusset plates and recommended that the capacity of these plates on non-redundant steel truss bridges be verified. The purpose of this study is to examine the buckling behaviour of steel gusset plates in greater detail, accounting for parameters that were not explicitly included in the guidelines, such as initial deformations of the gusset plate, stiffness of the framing members, load distribution from the framing members to the plate and load eccentricity. For this purpose, a finite-element model of a gusset plate was developed and verified against experimental measurements. Results show that, for in-plane compressive loads with no moment and no eccentricity, the FHWA guidelines for load rating are conservative and safe for initial out-of-plane deformations up to one plate thickness.

Wind-Pressure Coefficients on Low-Rise Building Enclosures Using Modern Wind-Tunnel Data and Voronoi Diagrams

AbstractExternal pressure coefficients specified in the ASCE 7-10 Standard, used to determine design wind pressures for the components and cladding of buildings, are developed from wind tunnel test...

Wind Load Factors for Use in the Wind Tunnel Procedure

AbstractPublished standards may be incomplete because they provide no guidance on wind load factors appropriate for use with the wind tunnel procedure. The purpose of this paper is to contribute to...

Analysis of Wind Pressure Data on Components and Cladding of Low-Rise Buildings

AbstractThis paper presents a methodology for analyzing wind pressure data on cladding and components of low-rise buildings. The aerodynamic force acting on a specified area is obtained by summing ...

Estimating Peaks of Stationary Random Processes: A Peaks-over-Threshold Approach

AbstractEstimating properties of the distribution of the peak of a stochastic process from a single finite realization is a problem that arises in a variety of science and engineering applications....

The Use of Wind Tunnel Measurements in Building Design

The ASCE 7-10 Standard contains provisions on the use of the wind tunnel, but those provisions are incomplete. For this reason estimates of structural response to wind can vary significantly depending upon the laboratory that provides them. This has been the case, for example, for New York City’s World Trade Center’s twin towers, for which such differences have exceeded 40 % (NCSTAR 1-2, Appendix D, 2004). While the emphasis here is on the testing of buildings in wind tunnels, it is therefore necessary to review the inter-related elements involved in the estimation of the response of buildings to wind, namely, micrometeorology, aerodynamics, similitude, wind climatology, statistics, and structural reliability. The chapter also discusses the validation of wind tunnel measurements, and their application to low-rise and tall buildings, and concludes with a description of a timedomain method for designing structural members known as Database-Assisted Design. For additional materials on wind tunnel testing the reader is referred to, e.g., ASCE (1999), Reinhold (1982), and Simiu (2011).

Nonlinear Database-Assisted Design Leads to ''Greener'' Steel Buildings

This paper presents an improved method to design buildings to resist high wind. The method consists of using databases of pressures measured in wind tunnel tests and applying these pressures in nonlinear structural analyses, hence the name nonlinear database-assisted design (NLDAD). Available databases of experimental measurements provide structural designers with an envelope of peak loads for all critical sections of a structure, and thus greater confidence in the safety of the design than if a few idealized pressure distributions specified by building codes were used. Unlike earlier approaches, the approach used in this paper targets all potentially critical cross sections of the structure being designed. Precise knowledge of the load cases required enables optimization of the structure, thus leading to more efficient use of materials, which translates into lower cost and less demand on the environment, as well as improvement in safety. NLDAD is not proposed for routine office calculations, but rather for calculations intended to develop standards provisions that reflect more correctly than current methods based on linear response do, the capacity of structures to withstand wind and gravity loads. To illustrate the method, one frame of a steel warehouse originally designed to satisfy ASCE 7-93 wind loads, was investigated. Updated ASCE 7-02 loads were used in this investigation, as well as wind tunnel measurements. The paper describes the selection of load cases from the experimental database using a linear beam model. Next, a much more detailed finite-element model was analyzed under the selected load cases into the large displacement, post-yielding range, with account taken of local plate buckling and initial imperfections. By using NLDAD, improvement in wind resistance of 30% was achieved, at the cost of 3.6% increase in weight. Most of the performance improvement was attributable to structural modifications that were partly enabled by nonlinear analysis. Conversely, for the same wind resistance, a decrease in weight of 10% or so is possible with NLDAD. The governing load case from the wind tunnel pressure database confirms the validity of ASCE 7-02 pressures. When initial deformations are accounted for, the structure still passes ASCE 7-02 Standards only to the extent that wind load factors specified in the Standards may be construed to be associated with ultimate strength rather than allowable stress design. The margin of safety mentioned in ASCE 7-02 Commentary is overly optimistic.