Strategies for Wind Damage Mitigation—Summary

Wind damage to buildings and structures in the United States costs approximately $4 billion a year, mostly to nonengineered buildings. Civil engineers should help identify structural problems (weak links) in these buildings and effective ways to correct the problem so that improved building codes and better construction practices can result in a reduction of damage. Strategies for mitigation involve many facets, such as educating the public that much can be done to reduce wind damage with minor improvement of buildings and minor cost increases; disseminating research findings and new knowledge to engineers, architects, builders, contractors, insurance companies, building code officials, and the public; incorporating key research findings into building codes and common practice; improving code enforcement; providing incentives through insurance‐premium reduction; and intensifying research to identify the most effective and economical ways to improve building performance. An international effort to share information and knowledge in wind‐disaster mitigation—the concept of International Decade of Disaster Mitigation, proposed by Dr. Frank Press, President of the National Academy of Science—should also be part of a global strategy.     

Strategies for Mitigating Damage to Metal Building Systems

Hurricanes Camille (1969), Frederic (1979), and Elena (1985) subjected the Gulf coastal region to wind‐speed regimes at or near design level events. Additionally, during the time interval, the wind‐load provisions of ANSI A58.1 and the industrial standard for Metal Building Systems (MBMA) had undergone extensive revisions. Tens of thousands of steel‐framed, pre‐engineered buildings were affected by these three hurricanes, providing valuable field evidence to assess structural performance. The object of this paper is to review the damage patterns inflicted by these major storms and suggest mitigation strategies for reducing the damage to metal building systems. The structural performance of metal buildings is well understood, and, for the most part, adequate code provisions are currently in place to ensure satisfactory behavior in high winds. The unique manner in which metal buildings are engineered, fabricated, marketed, sold, and erected suggests that much of the effort needed to mitigate wind damage primarily falls on the shoulders of the franchised dealer or his engineer of record.     

Wind Design Problems with Building Structures During Construction

A great deal of damage and loss of property are caused by wind during construction. Partially‐completed structures and temporary works that provide support, access, or protection present the greatest risks. The damaging winds are usually much lower than the design wind loads for completed structures. The design wind speed for short‐term exposure, the drag and shielding coefficients for partially completed structures, and the required temporary strength and stability need to be examined. U.S. building codes and standards provide inadequate or no guidance at all. There is a need to investigate, define, and mitigate the wind‐created risks on construction projects.     

Deficiency Analysis of Coastal Buildings toward Storm Damage Reduction

Engineering services provided by one of the writers to property owners, insurance companies, attorneys, and others have resulted in a compilation of case studies, based on more than 1,000 site inspections, suitable to generate a database regarding various aspects of building performance. The scope of those services typically included identifying the cause and origin of damage to residential and commercial structures, as well as an estimation of the magnitude of damage sustained by those structures. The majority of those damaged structures was located in proximity to a coastal region and experienced recent exposure to a storm or other weather event. Compilation of data from those case studies allowed identification and ranking of the occurrence of chronic building problems. It has become apparent that building-related deficiencies often exist as a common feature in similar structures. Some of those recurring deficiencies could be eliminated with alternate building design, better construction practices, or proper routine maintenance procedures. Where applicable, proposed remedial solutions are presented for specific building deficiencies or problems identified.     

Building Orientation and Wind Effects Estimation

The methodology for estimating wind effects presented in this paper is based on the database-assisted design approach. It accounts for the effects of wind directionality, for the effects of the uncertainties in the parameters that determine wind effects, and for the effects of building orientation. The methodology yields estimates of wind effects that are far more realistic than those based on the conventional building code approach, which disregards uncertainties in those parameters, as well as the effects of wind directionality and building orientation, or accounts for these effects through the use of a blanket reduction factor. The pilot software on which the calculations presented in this paper are based is a first step toward modern computer-intensive electronic standards wherein wind loads can be calculated by using database-assisted reliability-based calculations of wind effects. We believe such standards will go a long way toward achieving significantly safer and more economical buildings in regions affected by strong winds.     

Review of Standard Practice for Wind‐Resistant Manufactured Housing

Manufactured homes are popular as single family dwellings because of their low cost per square foot (square meter) relative to conventional housing. Despite their popularity, there is concern for the significant wind losses reported each year, not to mention the accompanying injuries and deaths. Wind damage is primarily in the form of roof loss and tiedown∕foundation failures. Initiation of roof loss or tiedown∕foundation failure sometimes leads to sudden and total destruction of a manufactured home. Federally enforced wind‐load design criteria need to be reevaluated, but changes in construction practices to provide redundancy and ductility in the load‐resisting structural system will be more effective in improving the performance of housing in high winds. The use of ground anchors in the tiedown∕foundation system must be abandoned in favor of permanent foundations similar to those used in conventional housing construction. Permanent foundations are somewhat more expensive than the tiedown∕foundation system currently in use, but the effects of additional costs can be minimized with longterm financing.     

Causes of Collapse and Damage to Low-Rise RC Buildings in Recent Turkish Earthquakes

This study assesses performance objectives defined in the Turkish Earthquake Code (TEC) in order to make a realistic evaluation related to heavy damage and collapse reasons of reinforced concrete (RC) buildings that experienced severe earthquakes in Turkey. A series of three-dimensional RC buildings with different characteristics and representing low-rise structures damaged and collapsed in the earthquake areas is designed according to Turkish codes (Turkish Design Standards and Turkish Earthquake Code). Pushover analyses are carried out to determine nonlinear behavior of the buildings under earthquake loads. Building performances are determined by using the displacement coefficients method, which is a commonly used nonlinear static evaluation procedure for different seismic hazard levels defined in the TEC. The stipulated performance objectives in the TEC are checked in terms of plastic rotations and maximum story drift. From the results of this research, it can be concluded that low-rise RC buildings designed according to Turkish codes sufficiently provide for the performance objectives stipulated in the TEC. Reasons for the heavy damages and collapses of RC buildings during severe earthquakes are explained by commonly occurring themes (i.e., project errors, poor quality of construction, modifications of buildings, etc.).     

Wind Damage to Wood‐Frame Houses: Problems, Solutions, and Research Needs

Wood‐frame houses (light‐frame timber construction) suffer widespread losses in high winds. Improvements in construction techniques and practices can greatly reduce wind damage to such buildings. The most serious problem contributing to wind damage in wood‐frame houses is inadequate tie‐down of roofs. Other serious problems include inadequate tie‐down of wall frames to foundation, weak joints, lack of racking resistance, and sloppy construction practice. Simple and inexpensive means exist to correct most of these problems. Research needs include the development of better methodologies to analyze the response of wood‐frame houses, especially the response of joints, full‐scale testing of wood‐frame houses, testing of dissected joints, improved understanding of wind loads, and post‐disaster investigations focused on individual houses.     

Design of Low-Rise Buildings for Extreme Wind Events

Damages from hurricanes and various windstorm events represent a loss of several billions of dollars in the United States. A loss of $30 billion was attributed to Hurricane Andrew alone in Florida in 1993. In 2004 and 2005, Florida, Louisiana, Mississippi, and other locations in the southeast United States and the Caribbean saw an unprecedented wave of major hurricanes causing great destruction and property damage. This paper discusses the topic of home design for high winds and hurricanes, and sums up a recently completed practical research on this subject.     

Roof Damage in New Homes Caused by Hurricane Charley

Hurricane Charley was the first Category 4 hurricane to strike Florida after 1992. This paper presents results of a study to investigate the performance of 425 of 747 roofs of new homes in Punta Gorda Isles, a subdivision of Punta Gorda that was directly in the path of Hurricane Charley shortly after it made landfall. The homes examined were larger, concrete/clay tiled roof homes having irregular floor plans and complex roof configurations not explicitly addressed by prevailing wind load codes. Roof damage was evaluated using images from aerial photographs taken at an elevation of approximately 762?m?(2,500?ft.) Specialized software was used to quantify damage. Damage was classified based on tile loss area. The study showed that the vast majority of the roofs were either undamaged or sustained minor damage. Fewer than 14% were classified as damaged. The most common observed tile loss was along ridges, corners, or in the hip zone where negative uplift pressures are recognized to be the highest. Given the modest observed damage, prevailing methods for estimating wind loads for irregular buildings specified in codes may be adequate. Problems encountered may be best resolved through new details for attaching tiles on ridges, corners, and hip zone.     

Mitigation of Severe Wind Damage Related to Ground Transportation Systems

The assessment of the highest winds to be expected in a given location has been accomplished for well‐populated areas by long‐standing data‐keeping on the part of meteorological agencies and the exercise of extreme‐value statistical analysis of such data. The paper addresses only problems of fixed transportation structures, such as road signs and bridges, and not those of ground vehicles and their design. Such vehicles are highly vulnerable to winds greater than those related to their design forward velocities, and very sensitive to those winds having components across the direction of vehicle travel. Fixed structures must be designed to withstand the highest expected winds at their sites. This calls for a design appreciation of wind climatology, information on local terrain conditions, and proper formulation of the expressions for the wind forces acting on structures of particular configuration.     

Wind Damage to Airport: Lessons Learned

High winds at a maximum speed of 96 mph (43 m∕s) hit the Columbia Regional Airport in Missouri on June 17, 1985, causing heavy damage to parked aircraft, hangars, building glass windows, automobiles, and so on. A post‐disaster investigation reveals a wealth of information, such as the finding that the storm was a microburst, and not a tornado as it was originally classified, that the aircraft tiedown system was flawed, that a gravel road was the principal source of damage to cars parked at the airport terminal, that the gust factor of this type of wind is much higher than normally assumed for structural design, and so on. Additional findings are that the atmospheric pressure of the storm measured was greatly affected by the wind‐generated pressure of the building in which the barometer was housed, and that west is the predominant direction of high winds at this airport. Lessons learned from the investigation can be very helpful in reducing future wind damage at airports and in improving understanding of weather data pertaining to severe storms and how to use these data in engineering practice.     

Peak Non-Gaussian Wind Effects for Database-Assisted Low-Rise Building Design

Current procedures for estimating the peaks of the stochastic response of tall buildings to wind are based on the assumption that the response is Gaussian. Those procedures are therefore inapplicable to low-rise buildings, in which time histories of wind-induced internal forces are generally non-Gaussian. In this paper, an automated procedure is developed for obtaining from such time histories sample statistics of internal force peaks for low-rise building design and codification. The procedure is designed for use in software for calculating internal force time series by the database-assisted design approach. A preliminary step in the development of the procedure is the identification of the appropriate marginal probability distribution of the time series using the probability plot correlation coefficient method. The result obtained is that the gamma distribution and a normal distribution are appropriate for estimating the peaks corresponding, respectively, to the longer and shorter tail of the time series’ histograms. The distribution of the peaks is then estimated by using the standard translation processes approach. It is found that the peak distribution can be represented by the Extreme Value Type I (Gumbel) distribution. Because estimates obtained from this approach are based on the entire information contained in the time series, they are more stable than estimates based on observed peaks. The procedure can be used to establish minimum acceptable requirements with respect to the duration and sampling rate of the time series of interest, so that the software used for database-assisted design will be both efficient and accurate.     

Construction of a Semi‐Prefabricated Masonry Facade

One of the crucial problems that faces designers, construction managers, general contractors, and subcontractors is creating the most appealing facade of a building at the most cost‐effective price, while satisfying an owner's goal of exploiting the enclosed space to maximum advantage. A brick facade has long been considered a durable and aesthetic solution for the exterior walls. A stud wall with gypsum board sheathing is today's most economical and widely used interior perimeter material. The development of innovative construction techniques that combine this exterior facade with interior perimeter materials in the most cost‐effective and time‐effective manner is the object of continuing trial and error. The industrialization of construction components has long been considered but, as yet, is not widely used, although its future appears bright. This paper analyzes the advantages of a semi‐prefabricated facade based on specific experience.     

Probabilistic Approaches for Pavement Fatigue Cracking Prediction based on Cumulative Damage Using Miner’s Law

In mechanistic-empirical (M-E) pavement design, pavement damage is modeled as a random variable with a pre-specified distribution (normal or lognormal). The extent of fatigue cracking in terms of percentage cracking is computed as the probability of cumulative damage exceeding unity. This paper provides a methodological framework for characterizing damage distribution under mixed traffic loading (multiple strain levels) with an improved forecast of traffic spectrum based on renewal theory. Using the linear Miner’s law for damage accumulation, analytical representation of damage distribution is obtainable owing to the proportional relationship between maximum tensile strain of pavement and traffic load under linear elasticity condition. Numerical computation shows that percent of cracking from derived damage distribution is greater than that from hypothetical normal or lognormal distributions traditionally used in the M-E pavement design. The method developed here and the derived model can be used in pavement design and pavement management systems.     

Gable-End Wall Stability in Florida Hurricane Regions, 10-Year Review: Post-Hurricane Andrew (1992) to Florida Building Code (2002)

Current reinforced masonry wall construction design practice in residential gable ends was reviewed for compliance with the Standard Building Code and ASCE 7-93 wind provisions. The investigation team reviewed 31 residential structures built in the state of Florida after Hurricane Andrew (1992) and before adoption of the Florida Building Code (2002). The existing bracing techniques used to support the gable-end wall were found inadequate to resist wind-induced suction forces defined according to the applicable building codes. The controlling parameters were the spacing of reinforcing pilaster columns and the methods of lateral support along the top of the masonry wall system. The investigation led in part to revisions in the Florida Building Code with respect to the lateral bracing of gable-end wall systems.     

Engineering Judgment and the Design That Got Away

This paper examines an ethical dilemma related to the residential construction industry in Florida, where homes must be engineered to withstand extreme load conditions induced during high wind events. Overwhelming contractor pressure to minimize construction costs has resulted in the propagation of inadequate construction designs. The overwhelming adoption of these inadequate designs weakens the integrity of our industry, creating the impression that market pressure can influence our judgment despite conflicting results gained through engineering analysis. This paper illustrates the frailty of engineering judgment as a design fundamental. Further, it raises the question as to what extent professional engineers should substitute engineering judgment for concrete evidence such as numerical analysis or experimental verification.     

Glass Breakage Tests under Fluctuating Wind Loads

The current North American design codes for wind loads have dealt with the unique characteristics of glass using the observed failure mechanism of static fatigue, which is based on the concept of damage accumulation as described by Brown’s integral. However, both the load resistance and the design loads have aspects that have not been fully validated because of available but limited experimental results, particularly with regard to fluctuating load patterns. With the recent development of a sophisticated pressure-loading device, precise, time-varying wind loads as well as conventional ramp loading were applied to annealed glass plates in this study. The measured results were consistent with Brown’s integral, confirming the conversion method from realistic wind-load time histories to equivalent static loads.     

Simplified Model for Evaluating Damage Potential of Buildings Adjacent to a Braced Excavation

This paper presents a simplified model for evaluating damage potential of a building adjacent to a braced excavation. New developments include several component models for estimating the lateral ground movement profile, angular distortion and lateral strain in a building, and damage potential of a building adjacent to an excavation. These new developments along with an existing model for the vertical ground movement profile are integrated into the proposed simplified model. Case histories are used to verify the developed simplified model. Furthermore, the uncertainty in the developed model is quantified, which enables a probabilistic assessment of the excavation-induced building damage potential. An example probabilistic assessment of building damage potential is presented.