Abstract
Accurate load evaluation is essential in any performance-based design. Design wind speeds and associated wind loads are well defined for synoptic boundary layer winds but not for thunderstorms. The method presented in the current study represents a new approach to obtain design wind speeds associated with thunderstorms and their gust fronts using historical data and Monte Carlo simulations. The method consists of the following steps (1) developing a numerical model for thunderstorm downdrafts (i.e., downbursts) to account for storm translation and outflow dissipation, (2) utilizing the model to characterize previous events and (3) extrapolating the limited wind speed data to cover life-span of structures. The numerical model relies on a previously generated CFD wind field, which is validated using six documented thunderstorm events. The model suggests that 10 parameters are required to describe the characteristics of an event. The model is then utilized to analyze wind records obtained at Lubbock Preston Smith International Airport (KLBB) meteorological station to identify the thunderstorm parameters for this location, obtain their probability distributions, and utilized in the Monte Carlo simulation of thunderstorm gust front events for many thousands of years for the purpose of estimating design wind speeds. The analysis suggests a potential underestimation of design wind speeds when neglecting thunderstorm gust fronts, which is common practice in analyzing historical wind records. When compared to the design wind speed for a 700-year MRI in ASCE 7-10 and ASCE 7-16, the estimated wind speeds from the simulation were 10% and 11.5% higher, respectively.
Abstract
One of the next frontiers in structural wind engineering is the design of tall buildings using performance-based
approaches. Currently, tall buildings are being designed using provisions in the building codes and standards to meet an
acceptable level of public safety and serviceability. However, recent studies in wind and earthquake engineering have
highlighted the conceptual and practical limitations of the code-oriented design methods. Performance-based wind design
(PBWD) is the logical extension of the current wind design approaches to overcome these limitations. Towards the development
of PBWD, in this paper, we systematically review the advances made in this field, highlight the research gaps, and provide a
basis for future research. Initially, the anatomy of the Wind Loading Chain is presented, in which emphasis was given to the
early works of Alan G. Davenport. Next, the current state of practice to design tall buildings for wind load is presented, and its
limitations are highlighted. Following this, we critically review the state of development of PBWD. Our review on PBWD
covers the existing design frameworks and studies conducted on the nonlinear response of structures under wind loads.
Thereafter, to provide a basis for future research, the nonlinear response of simple yielding systems under long-duration
turbulent wind loads is studied in two phases. The first phase investigates the issue of damage accumulation in conventional
structural systems characterized by elastic-plastic, bilinear, pinching, degrading, and deteriorating hysteretic models. The second
phase introduces methods to develop new performance objectives for PBWD based on joint peak and residual deformation
demands. In this context, the utility of multi-variate demand modeling using copulas and kernel density estimation techniques is
presented. This paper also presents joined fragility curves based on the results of incremental dynamic analysis. Subsequently,
the efficiency of tuned mass dampers and self-centering systems in controlling the accumulation of damage in wind-excited
structural systems are investigated. The role and the need for explicit modeling of uncertainties in PBWD are also discussed with
a case study example. Lastly, two unified PBWD frameworks are proposed by adapting and revisiting the Wind Loading Chain.
This paper concludes with a summary and a proposal for future research.
Key Words
performance-based wind design; wind loading chain; damage accumulation; joined fragility curves; copulas;
kernel density estimation; incremental dynamic analysis; tuned mass dampers; self-centering systems
Address
Matiyas A.: Department of Civil and Environmental Engineering, Western University, London, Canada/ School of Engineering, University of British Columbia, Okanagan, Canada
Bezabeh, Girma T. Bitsuamlak : Department of Civil and Environmental Engineering, Western University, London, Canada
Solomon Tesfamariam: School of Engineering, University of British Columbia, Okanagan, Canada
Abstract
The wind design of buildings is typically based on strength provisions under ultimate loads. This is unlike the
ductility-based approach used in seismic design, which allows inelastic actions to take place in the structure under extreme
seismic events. This research investigates the application of a similar concept in wind engineering. In seismic design, the elastic
forces resulting from an extreme event of high return period are reduced by a load reduction factor chosen by the designer and
accordingly a certain ductility capacity needs to be achieved by the structure. Two reasons have triggered the investigation of this
ductility-based concept under wind loads. Firstly, there is a trend in the design codes to increase the return period used in wind
design approaching the large return period used in seismic design. Secondly, the structure always possesses a certain level of
ductility that the wind design does not benefit from. Many technical issues arise when applying a ductility-based approach under
wind loads. The use of reduced design loads will lead to the design of a more flexible structure with larger natural periods. While
this might be beneficial for seismic response, it is not necessarily the case for the wind response, where increasing the flexibility
is expected to increase the fluctuating response. This particular issue is examined by considering a case study of a sixty-fivestory high-rise building previously tested at the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario
using a pressure model. A three-dimensional finite element model is developed for the building. The wind pressures from the
tested rigid model are applied to the finite element model and a time history dynamic analysis is conducted. The time history
variation of the straining actions on various structure elements of the building are evaluated and decomposed into mean,
background and fluctuating components. A reduction factor is applied to the fluctuating components and a modified time history
response of the straining actions is calculated. The building components are redesigned under this set of reduced straining
actions and its fundamental period is then evaluated. A new set of loads is calculated based on the modified period and is
compared to the set of loads associated with the original structure. This is followed by non-linear static pushover analysis
conducted individually on each shear wall module after redesigning these walls. The ductility demand of shear walls with
reduced cross sections is assessed to justify the application of the load reduction factor "R".
Abstract
In the design of buildings, lateral loading is one of the most important factors considered by structural designers.
The concept of performance-based design (PBD) is well developed for seismic load. Whereas, wind design is mainly based on
elastic analysis for both serviceability and strength. For tall buildings subject to extreme wind load, inelastic behavior and
application of the concept of PBD bear consideration. For seismic design, current practice primarily presumes inelastic behavior
of the structure and that energy is dissipated by plastic deformation. However, due to analysis complexity and computational
cost, calculations used to predict inelastic behavior are often performed using elastic analysis and a response modification factor
(R). Inelastic analysis is optionally performed to check the accuracy of the design. In this paper, a framework for application of
an R factor for wind design is proposed. Theoretical background on the application and implementation is provided. Moreover,
seismic and wind fatigue issues are explained for the purpose of quantifying the modification factor R for wind design.
Key Words
wind load; seismic load; inelastic behavior; R factor; performance-based design
Address
Hamidreza AlinejadSeung Yong Jeong and Thomas H.-K. Kang: Dept. of Architecture and Architectural Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
Abstract
The first step of performance-based design for transmission lines is the determination of wind fields as well as wind
loads, which are largely depending on local wind climate and the surrounding terrain. Wind fields in a mountainous area are very
different with that in a flat terrain. This paper firstly investigated both mean and fluctuating wind characteristics of a typical
mountainous wind field by wind tunnel tests and computational fluid dynamics (CFD). The speedup effects of mean wind and
specific turbulence properties, i.e., turbulence intensity, power spectral density (PSD) and coherence function, are highlighted.
Then a hybrid simulation framework for generating three dimensional (3D) wind velocity field in the mountainous area was
proposed by combining the CFD and proper orthogonal decomposition (POD) method given the properties of the target
turbulence field. Finally, a practical 220 kV transmission line was employed to demonstrate the effectiveness of the proposed
wind field generation framework and its role in the performance-based design. It was found that the terrain-induce turbulence
effects dominate the performance-based structural design of transmission lines running through the mountainous area.
