Database-assisted Design Research Articles

Performance evaluation of high-rise buildings using database-assisted design approach

In recent years, performance-based design (PBD) has gained attention and is sought to be the benchmark approach in the field of wind engineering. While the concept of performance-based design is well-accepted in earthquake engineering, it is yet to be embraced for the design of buildings to resist severe wind loads. This paper introduces a framework for the performance-based wind design (PBWD) of tall steel buildings using a time domain analysis that keeps the process of wind effects and the structural design process integrated, transparent, and fully auditable. From the perspective of PBWD, the main objective is to achieve a desirable performance level for a given hazard level, i.e., mean recurrence interval of extreme wind. The wind effects are directly related to the mean annual return of wind through a well-accepted simulation approach. A 180 m tall standard CAARC building is used for the case study to illustrate the proposed methodology. The wind load time histories are determined using the pressure tap data on exterior faces of the building measured in the wind tunnel. With the calculated wind loads, nonlinear dynamic analysis is conducted with various wind directions and mean wind speeds based on database-assisted design (DAD) approach. The key performance measures such as demand-to-capacity indices, inter-story drift, damage deformation index, and floor accelerations are calculated as a function of wind directions and mean wind speed. The obtained responses are used in conjunction with a local wind climatological database to determine the extreme wind effects for any specific mean recurrence interval. The performance of the steel building is evaluated for three performance criteria, including occupant comfort, operational, and continuous occupancy. The conducted performance assessment reveals that building fails to satisfy the serviceability requirement of drifts. However, the building satisfies the requirements for the occupant comfort and operational performance levels for strength design, while it also satisfies the continuous occupancy, limited interruption in Risk category II. The result reveals that the proposed framework provides realistic assessment of performance of the building incorporating the wind directionality and return period of the wind speeds.

Wind Load Evaluation of Low-Rise Residential Buildings for Coastal Communities Using Database-Assisted Design Method

Wind Load Evaluation of Low-Rise Residential Buildings for Coastal Communities Using Database-Assisted Design Method

Computational method in database-assisted design for wind engineering with varying performance objectives

The concept of Performance objective assessment is extended to wind engineering. This approach applies using the Database-Assisted Design technique, relying on the aerodynamic database provided by the National Institute of Standards and Technology (NIST). A structural model of a low-rise building is analyzed to obtain influence coefficients for internal forces and displacements. Combining these coefficients with time histories of pressure coefficients on the envelope produces time histories of load effects on the structure, for example knee and ridge bending moments, and eave lateral drift. The peak values of such effects are represented by an extreme-value Type I Distribution, which allows the estimation of the gust wind speed leading to the mean hourly extreme loading that cause specific performance objective compromises. Firstly a fully correlated wind field over large tributary areas is assumed and then relaxed to utilize the denser pressure tap data available but with considerably more computational effort. The performance objectives are determined in accordance with the limit state load combinations given in the ASCE 7-16 provisions, particularly the Load and Resistance Factor Design (LRFD) method. The procedure is then repeated for several wind directions and different dominant opening scenarios to determine the cases that produce performance objective criteria. Comparisons with two approaches in ASCE 7 are made.

Effects of aerodynamic pressure tap layout and resolution on estimated response of high-rise structures: A case study

This study examines the influence of pressure tap density and layout on estimated wind effects of a 47-story steel building for which the Database-Assisted Design procedure is used to calculate the base shears, base overturning moments, member Demand-to-Capacity Indexes (DCIs), inter-story drift ratios, and floor accelerations. From an original tap layout (20 rows by 5 columns, total 100 taps per façade), a total 16 tap layout cases were created varying vertical and horizontal tap densities. The influence of the tap density on the estimated wind effects of interest was then investigated. In most cases the calculated structural response is significantly more influenced by the horizontal than by the vertical tap density. The influence of the tap density was found to be strongest on the estimated base torsion, followed by the member DCIs, the base shears, and the base overturning moments. The acceptable pressure tap density depends on the structural response of interest. The results show that the current practice of considering global quantities like the overturning moment and/or the base shear as indicators of the adequacy of tap resolution for structural design can be misleading.

Verification of ASCE 7-16 Pressure Coefficients and Database-Assisted Design of Purlins and Girts Accounting for Wind Directionality.

For the database-assisted design (DAD) of low-rise building purlins and girts, a method is proposed that explicitly accounts for wind directionality by using directional wind tunnel measurements, directional wind speed data, and publicly available software. The method consists of four steps: (1) assignment of wind loads induced by a unit directional wind speed on purlins and girts from pressure taps and their tributary areas; (2) development of bending moment and shear force influence coefficients for line loads on purlins and girts; (3) multiplication of loads from step 1 by influence coefficients from step 2 and estimation of the peak bending moments and shear forces thus obtained; and (4) use of nonparametric statistics to calculate peak moments and shear forces with a specified mean recurrence interval for various building orientations and accounting for wind directionality. For one example of wind effects on purlins, (1) comparison of the Envelope Method in ASCE 7-16 (taken as 100%) with the most demanding aerodynamic case from wind tunnel tests shows differences ranging between +10% and -25%; and (2) comparison of the ASCE 7-16 method accounting for the wind directionality factor Kd with directional wind loads using nonparametric statistical methods shows differences ranging between +21% and -25%. The unconservatism (+) of ASCE 7-16 is thus worse after Kd is applied. The proposed method is based on the rigorous DAD approach, accounts explicitly for the actual directional wind loading, entails no onerous computational requirements, and typically results in more economical designs while assuring risk-consistent safety.

The Analogs of Temporin-GHa Exhibit a Broader Spectrum of Antimicrobial Activity and a Stronger Antibiofilm Potential against Staphylococcus aureus.

The abuse of antibiotics has led to the emergence of multidrug-resistant bacteria, which is becoming a serious worldwide problem people have to face. In our previous study, temporin-GHa (GHa) cloned from Hylarana guentheri showed antimicrobial activity against Gram-positive bacteria. In order to improve its therapeutic potential, we used a template-based and a database-assisted design to obtain three derived peptides by replacing the histidine at both ends of GHa with lysine, which exhibited faster and stronger bactericidal activity and a broader spectrum than the parent peptide. GHaK and GHa4K targeted to the bacterial membrane to exert their antibacterial activities at a faster membrane damage rate. The derived peptides inhibited the initial adhesion and the formation of Staphylococcus aureus biofilms, and eradicated the mature biofilms, which indicated that the derived peptides effectively penetrated the biofilm and killed bacteria. The therapeutic index (TI) and cell selectivity index (CSI) of the derived peptides increased significantly, which means a broader therapeutic window of the derived peptides. The derived peptides with improved activity and cell selectivity have the potential to be the promising candidates for the treatment of S. aureus infections. Our research also provides new insights into the design and development of antimicrobial peptides.

Wind Effects on a Tall Building with Square Cross-Section and Mid-Side Base Columns: Database-Assisted Design Approach.

This paper illustrates the application of the database-assisted design (DAD) method to the wind design of high-rise buildings. The paper uses publicly available wind tunnel data and DAD procedures to compare responses to (1) corner winds and (2) face winds of a high-rise building of square cross-section supported by a central core column and four mid-side legs. The responses being considered consist of overturning moments, and of demand-to-capacity indexes (DCIs) of selected members, including multistory chevron braces. The analysis accounts for structural dynamics and second-order load-deformation effects. The results show that corner winds are less demanding than face winds, both globally (overturning moments) and locally (DCIs). The along-wind and across-wind overturning moments in the corner wind case are about 20% and 50% lower, respectively, than their counterparts in the face-wind case. The peak axial forces in the legs (peak refers to absolute value) and the peak DCIs in the mid-side mast columns (continuation of the legs) induced by corner winds are lower by 20%-30% than their counterparts due to face winds. The investigation confirms that the building code of the City of New York in effect in the early 1970s can be interpreted as meaning that the design for wind of structures with a square shape in plan may be performed by assuming the wind loads to act normal to a face of the building. The building analyzed in this paper is similar to the Citicorp Building (completed in 1977, later renamed Citigroup Center, now called 601 Lexington) and the results of the analyses presented herein suggest that a re-examination of the history of the Citicorp Building design and retrofit may be warranted.

Equivalent static wind loads vs. database-assisted design of tall buildings: An assessment

Recent developments in pressure measurement technology, and unprecedented “big data” capabilities, have enabled the development of Database-Assisted Design (DAD), a powerful innovative approach to the design of tall buildings for wind. DAD eliminates unwieldy back-and-forth interactions between the wind and the structural engineer, needed in traditional practices if iterative designs are performed. Some structural engineers have shown interest in an alternative approach that uses equivalent static wind loads (ESWLs) in lieu of DAD. Such an approach is warranted if ESWLs induce in structural members demand-to-capacity indexes (DCIs) approximately equal to their peak counterparts obtained by DAD. This paper presents and assesses a simple procedure for calculating such ESWLs. The procedure uses an effective multiple points-in-time (MPIT) method for estimating combined peak wind effects, and accounts for wind directionality. A case study is presented that uses both the ESWL and DAD procedures, with the latter providing the requisite benchmark results. DCIs obtained from ESWLs based on the use of ten points-in-time (corresponding to 60 wind loading cases) were significantly closer to the benchmark DAD values than their counterparts based on the use of, e.g., four points-in-time (corresponding to 24 wind loading cases). For the building considered in this case study, ESWL-based design DCIs approximated to within approximately 3% the DCIs yielded by DAD. The approximation was found to be poorer for cases in which a single unfavorable wind direction is strongly dominant. The ESWL procedure is not applicable in its present form to structures with complex shapes. In all cases, the DAD procedure is the safest and most risk-consistent design option.

Progressive failure analysis of low-rise timber buildings under extreme wind events using a DAD approach

This paper discusses the interaction of low-rise timber buildings with wind loads under significant wind events such as hurricanes. The proposed analysis methodology is capable of predicting the progressive failure of low-rise buildings as a result of the wind-structure interaction for a cost-effective design. It will also assist in evaluating the wind intensity from the observed damage state of buildings. Two deterministic finite-element (FE) models are developed using ANSYS for the full-scale numerical simulation. The first model with a simple building configuration is used for the validation of a numerical modeling methodology in the ultimate failure range. It also serves to validate the proposed progressive failure analysis process via the calibration from the corresponding wind tests that can simulate failures. Then, this analysis methodology is used to study the successive stages of damage on the second model to unveil its potential applications on a more representative residential buildings in U.S. Spatiotemporally varying wind loads are applied with the purpose of expanding the application of database-assisted design (DAD) approach from the linear range to the nonlinear range and finally to the stage-wise failures, which is a necessity of the vulnerability assessment and is critical for the damage and loss prediction for the insurance industry.

Assessment of ASCE 7-10 for wind effects on low-rise wood frame buildings with database-assisted design methodology

The design wind pressure for low-rise buildings in the ASCE 7-10 is defined by procedures that are categorized into the Main Wind Force-Resisting System (MWFRS) and the Components and Cladding (C&C). Some of these procedures were originally developed based on steel portal frames of industrial buildings, while the residential structures are a completely different structural system, most of which are designed as low-rise light-frame wood constructions. The purpose of this study is to discuss the rationality (or irrationality) of the extension of the wind loads calculated by the ASCE 7-10 to the light-frame wood residential buildings that represent the most vulnerable structures under extreme wind conditions. To serve this purpose, the same approach as used in the development of Chapter 28 of the ASCE 7-10 that envelops peak responses is adopted in the present study. Database-assisted design (DAD) methodology is used by applying the dynamic wind loads from Louisiana State University (LSU) database on a typical residential building model to assess the applicability of the standard by comparing the induced responses. Rather than the postulated critical member demands on the industrial building such as the bending moments at the knee, the maximum values at the critical points for wood frame buildings under wind loads are used as indicators for the comparison. Then, the critical members are identified through these indicators in terms of the displacement or the uplift force at connections and roof envelope. As a result, some situations for each of the ASCE 7 procedures yielding unconservative wind loads on the typical low-rise residential building are identified.

Effect of wind-induced internal pressure on local frame forces of low-rise buildings

Given the significant role of internal pressures in the wind-induced loading of low-rise buildings, their correct estimation is critical for the accurate determination of the net (external plus internal) wind effects. This paper presents results of an investigation conducted to study the effect of wind-induced internal pressures on structural frame forces on low-rise buildings with single or multiple dominant openings. Models from the National Institute of Standards and Technology (NIST) aerodynamic database with internal pressure measurements were used. Large-scale experiments were also conducted in the Wall of Wind (WOW) facility at Florida International University (FIU) using a model with multiple openings. Calculations of frame forces were performed using the Database-Assisted Design (DAD) methodology. It was found that internal pressure significantly increases the forces induced by wind with the most unfavorable direction on the frames located close to the openings. However, its effect on the frames located away from the openings was smaller. Effects of internal pressure also varied between different cross-sectional locations of the same frame, depending upon the correlation between forces induced by external and internal pressures. For the highest net frame forces, the reduction factor applied to the response induced by internal pressures, that accounts for the imperfect correlation between the external and internal pressures, was found to be approximately 0.85. Comparison between frame forces calculated using experimentally measured internal pressures and their counterparts evaluated by using ASCE 7–10 provisions for internal pressures showed that the latter result in unconservative estimates of frame forces in both enclosed and partially enclosed buildings. An additional significant result is that the ASCE 7 classification of buildings with equally sized windward and leeward openings as enclosed buildings can lead to the underestimation of net frame responses. It is therefore proposed that this classification be changed to reflect the appropriate internal pressure effects.

Design of rigid structures for wind using time series of demand-to-capacity indexes: Application to steel portal frames

Estimates of wind effects on rigid buildings by database-assisted design (DAD) methods can be far more accurate than those based on information available in standards. An upgraded version of DAD is presented that streamlines the wind engineering/structural engineering components of the design process by allowing the direct computation of Demand-to-Capacity Indexes (DCIs). The computation achieves the rigorous combination of imperfectly correlated time series of wind forces and effects, thus eliminating errors due to subjective estimates of combined effects. The basic approach being presented is applicable to any rigid building. This paper focuses on simple buildings with gable roofs, portal frames, and bracing parallel to the ridge. Useful features of this work include: the capability to use the two largest building aerodynamics databases available worldwide; the use of large simulated extreme wind databases for hurricane- and non-hurricane-prone regions; a novel interpolation scheme allowing the design of buildings with dimensions not represented in the databases; an effective multiple-points-in-time algorithm for estimating peaks; and parameter-free methods for estimating DCIs with specified mean recurrence intervals. Case studies indicated that the proposed interpolation scheme was satisfactory. The results obtained confirm: (i) published results which show that the ASCE 7-10 envelope procedure can significantly underestimate wind effects; (ii) the mutual consistency for practical purposes of the two aerodynamic databases being used; and (iii) DAD’s potential for practical use in structural design. The software developed for the implementation of the procedure is available at http://www.itl.nist.gov/div898/winds/iterative_design/wind_design.htm. A user’s manual is available at http://nvlpubs.nist.gov/nistpubs/TechnicalNotes/NIST.TN.1908.pdf.

An estimate of tornado loads on a wood-frame building using database-assisted design methodology

Thunderstorms and related tornadoes caused over $25 billion in damages in 2011, the majority of which occurred to residential structures. Over 13,000 homes were damaged or destroyed by two tornadoes in Tuscaloosa and Joplin alone. Such substantial losses should not be surprising because as yet, no design guidelines exist for tornadoes, and with the current wind provisions in accepted building codes there is limited capacity in any wood-framed structure to withstand tornado loads. The objective of this current study is to develop appropriate design structural reactions for light-framed wood structures that is subjected to tornado loads. The study uses tornado simulator-generated surface pressure data from a fully sealed 1:100 scale gable roof model, experimentally-determined structural influence functions, and a modified database-assisted design (DAD) methodology to predict the reactions. Forces are established at structural connections for a tornado with peak wind speeds of 60.3m/s (135mph). Results are compared against structural reactions due to straightline winds with an identical peak wind speed, as determined using ASCE 7–10 wind pressure distributions. It is shown that for a sealed building (i.e., no pressure equalization between the building interior and exterior), the peak shear forces under tornado loads are 1.8 times as strong for roof-to-wall connections and twice as strong for wall-to-foundation connections, as compared to those from ASCE 7–10 wind loads. The peak vertical loads on connections are even higher, nearly four times as high for the roof-to-wall and wall-to-foundation connections. Nearly 60% of the peak loads can be attributed to the assumption of a fully sealed building mode, which results in the full effect of the pressure drop within the vortex being experienced on all surfaces of the building.

Generation of Large Directional Wind Speed Data Sets for Estimation of Wind Effects with Long Return Periods

AbstractFor structures sensitive to wind directionality, methods for the estimation of wind effects require the use of time series of directional wind speeds that cover time periods exceeding the length of the mean recurrence interval (MRI) of interest to the design. This study proposes a procedure for generating such time series from relatively short wind data sets. First, an algorithm is developed for estimating the parameters of the distributions of the directional wind speeds, given that the size of the data sample within one or more directional sectors can in some instances be too small for statistical inference purposes. Once the distribution parameters are estimated, a simple Monte Carlo procedure is used for data generation. The wind speed data being generated can be used within the framework of the database-assisted design approach to determine wind effects on buildings by accounting for wind directionality.

Using instrumented small-scale models to study structural load paths in wood-framed buildings

A large 1/3-scale model of a light-framed wood structure was constructed in order to study the structural reactions to wind loads in a three-dimensional model of a residential building. Thirty load cells measuring structural reactions at roof-to-wall and wall-to-foundation connections were used to determine influence functions in response to surface pressures generated by extreme winds. The influence functions are used in a database-assisted design (DAD) methodology to estimate failure loads in structures subjected to spatio-temporally varying wind loads. Current numerical methods based on 2D component models alone can lead to underestimated failure loads and inadequate designs. This paper describes the approach to develop the physical models and to validate their applicability to full-scale houses. Non-dimensional modeling techniques are explained, and scale model material properties for sheathing, wood-framing members, nails and truss-plate connections are provided. The need for a robust experimental method for determining influence functions is critical as load distributions are unpredictable in these structurally indeterminate systems. Further, the 1/3-scale physical models provide an economical approach to generate a large dataset of empirically-based models needed to cover a wide variety of geometrically complex houses and to calibrate non-linear numerical analysis programs for further DAD studies. The approach introduced in this study can be applied to more complex roof geometries and also to study the combined effects of horizontal and vertical wind load distributions in wood buildings.

Practical estimation of veering effects on high-rise structures: a database-assisted design approach

Atmospheric boundary layer winds experience two types of effects due to friction at the ground surface. One effect is the increase of the wind speeds with height above the surface. The second effect, called the Ekman layer effect, entails veering - the change of the wind speed direction as a function of height above the surface. In this study a practical procedure is developed within a database-assisted design (DAD) framework that accounts approximately for veering effects on tall building design. The procedure was applied in a case study of a 60-story reinforced concrete building, which also considered the dependence of veering effects on the orientation of the building. Comparisons are presented between response estimates that do not account for veering, and account for veering conservatively. For the case studied in this paper veering effects were found to be small.

Interpolation of pressure coefficients for low-rise buildings of different plan dimensions and roof slopes using artificial neural networks

Database-assisted design (DAD) is emerging as an important tool to design buildings for wind effects. However, there is a need for robust interpolation methods for pressure coefficients to extend the range of conditions beyond those in the aerodynamic database from wind tunnel experiments. An interpolation methodology, using artificial neural networks (ANN), was developed to include variable plan dimensions and roof slopes in the set of parameters considered in earlier interpolation studies. In addition to expanding the capabilities for interpolation, the new models improved predictions in the lee of the ridges for gable-roofed and low-rise buildings.

High-Rise Reinforced Concrete Structures: Database-Assisted Design for Wind

Advances in wind pressure measurement and computer technology have made time-domain analyses of wind effects on high-rise structures possible in recent years. Time-domain solutions use aerodynamic and wind climatological databases and provide full phase information on wind-induced response that is lost in the frequency-domain approach; therefore, they can account rigorously for the superposed effects of any number of modes of vibration of any shape; for mode coupling; for wind directionality effects; and for the joint contributions of axial forces, bending moments, and shear forces in interaction equations used for structural design. Unlike the frequency-domain approach, in the time-domain approach, the process of determining wind effects and the structural design process, referred to jointly as database-assisted design (DAD), are integrated, transparent, and fully auditable. The objective of this study is to present the DAD approach as applied to high-rise reinforced concrete (RC) buildings. Given the ti...

Database-assisted design methodology to predict wind-induced structural behavior of a light-framed wood building

This study investigates the applicability of the database-assisted design (DAD) methodology to predict structural reactions in a light-framed wood structure subjected to fluctuating wind pressures. Structural influence functions were determined on a 1/3-scale light-frame wood structure, which was then subjected to a wind flow, while the surface pressures and structural reactions at roof-to-wall and wall-to-foundation connections were simultaneously recorded. There was a good agreement between the DAD-predicted structural reactions and experimentally measured reactions, confirming that the DAD method is suitable for predicting the structural reactions in light-frame wood buildings. Subsequently structural reaction time histories at several connections within the building were generated using a 1:50 scale wind tunnel model of the structure and the peak structural reactions determined using the DAD method and previously obtained influence functions. When the DAD-estimated reactions were compared with reactions predicted by the ASCE 7-05 main wind force resisting system (MWFRS) method, they showed the ASCE 7 reactions were highly non-conservative(i.e. smaller than the DAD method predictions), by as much as 39% at the gable end truss. The components and cladding method showed reasonable agreement with the DAD method for the gable end and first interior truss reactions but it too underestimated the reaction loads at the second and third interior trusses by 30% and 12% respectively.

Multivariate stochastic simulation of wind pressure over low-rise structures through linear model interpolation

The study focuses on the simulation of time histories of roof loading on low-rise structures for the purpose of determining design loads. Database assisted design (DAD) utilizes datasets from wind tunnel studies conducted over a variety of building shapes and in various roughness length conditions to provide an online database of time histories of structural loads. With the development of the DAD approach, it is of some importance to investigate simplified interpolation procedures in order to produce accurate pressure time histories for building shapes that have not been tested in the wind tunnel. It was hypothesized that the load time histories from the tested buildings could be used to extrapolate, interpolate, or otherwise infer the time histories of an untested building. This study investigates the efficacy of an interpolation scheme to infer the spectral and probabilistic descriptors of non-Gaussian correlated variables representing roof pressure coefficients based on those measured from wind tunnel tests on comparable but not identical building shapes. A multivariate non-Gaussian simulation method is used to generate time histories based on these interpolated models. Peak aggregate uplift statistics from the simulated loads compare favorably with experimental results. Limitations of the method are discussed.