Journal of Performance of Constructed Facilities

Buildings with large column-free floors or long-cantilevered structures can be susceptible to annoying vibrations due to everyday occupants’ activities such as walking. Computer modeling and analytical representation of building structural properties to predict the floor response subjected to excitations due to human activities are important issues that require further studies. Vibration testing and analysis of built structures can assist in more accurate estimation of structure dynamic properties. This paper presents the results of the modal testing conducted on an office building floor and analysis of the collected vibration measurements. It compares these results with the structural response using computer analyses. It also presents a sensitivity study to assess the importance of various structural parameters on the floor dynamic response. From the results presented, it is concluded that for the structure used in this study the raised flooring and nonstructural elements acted mainly as added mass and did not contribute to the floor damping. Conclusions are also made on the importance of various structural parameters on floor response and the analysis of the modal test results.

People are generally very sensitive to unexpected vibrations. Very small levels of building floor movements due to activities such as walking can become annoying to occupants. Accurate prediction, evaluation, and assessment of vibrations can greatly assist engineers and architects to design cost-effective building structures without such problems. In an attempt to clarify some of the issues related to this common serviceability problem, this paper presents a study of the various parameters used for the evaluation and assessment of building vibrations. Provisions of several current standards and design guides commonly used in North America and U.K. to evaluate and assess building vibrations as related to human perception and comfort are reviewed. These provisions are then applied using the vibrations measured during a number of walking tests conducted on a large cantilevered office building floor. Based on the results of this study, it is concluded that the vibration dose value (VDV) recommended by some standards and design guides provides a consistent and reasonable method of evaluation of building floor vibrations. In addition, new relationships between VDV, peak frequency-weighted acceleration, and crest factor are established to estimate the VDV.

A variety of terms are used to describe structural characteristics and concepts in the context of disproportionate collapse of structures. Some of these terms, namely collapse resistance, robustness, and vulnerability as well as redundancy, continuity, ductility, and integrity are discussed in this paper. It is shown that they are often used differently by different writers and that there is not always a general agreement today as to their precise meaning. This paper distinguishes these terms and the associated structural characteristics and suggests working definitions. Based thereupon, a general performance-based framework for preventing disproportionate collapse is presented and the methods available for enhancing the collapse resistance of a structure are discussed.

This study reviews research carried out in the U.K. to understand and improve the robustness of buildings when subject to blast from high explosive bombs. The work concentrates on the performance of ordinary civilian buildings, with particular emphasis on multistory buildings framed in either reinforced concrete or structural steelwork. At that time, some of the data were used to enhance conventional building construction, principally on government buildings, and some were used to aid postwar hardened building construction. The two main U.K. researchers whose work is the basis of this paper (Professor Sir Dermot Christopherson and Professor Lord Baker) identified a number of building weaknesses that led to local or progressive collapse, including connections in steel-framed buildings, as well as detailing weaknesses in reinforced concrete constructions. This paper reviews these features, as well as those that added resilience to bomb damage, with particular emphasis to the use of masonry infill panels in framed buildings. Much of the information on building performance is relevant to today’s engineers engaged in the design of buildings to survive blast from terrorist attacks involving a vehicle-borne improvised explosive device.

An earthquake sequence struck the province of L’Aquila (central Italy) leaving 305 dead, about 1,500 injured, and 29,000 homeless. Hundreds of low-intensity events occurred between January and March, 2009. The mainshock took place on April 6, 2009, and its epicenter was located at about 6 km southwest of L’Aquila town; three stronger aftershocks happened on April 7 and 9, 2009. This paper focuses on actual performance of older and more recently constructed building structures during the earthquake sequence. After the main seismological characteristics of the sequence are described, the most significant observed damages are analyzed and associated with theoretical failure modes for both reinforced concrete and unreinforced masonry buildings. Since older masonry structures were more seriously damaged, the effects of the earthquake are described with more emphasis to ordinary masonry and cultural heritage buildings (churches, palaces, and castles). In conclusion, a number of lessons may be learned from the L’Aquila earthquake sequence. Several features are highlighted and some proposals are given to upgrade the current methods of structural analysis, as well as the existing codes.

The prediction of the performance or service life of a building system and their components is a very complex task. Although many papers related to material and component durability have been published over the past two decades, they had a negligible impact on the development of an effective approach for durability design. ISO presents a valuable methodology based on the factor method in the area of service life estimation but it requires considerable local knowledge about degradation of components and materials. The factor method on the other hand is fairly simple but identifies the main parameters influencing service life. The result, however, is only a single figure for service life and does not take into account the variability of the processes involved. A lot of work is being done in the area of service life prediction, but there is very little that can be readily used by building asset managers. Hence, there is a great need to develop a simple model which can be easily calibrated and used. The model proposed here can be easily implemented by practitioners and would be of benefit to infrastructure managers of city councils.

A method is presented for obtaining condition index of corrosion distressed RC buildings. Method is developed using concepts of fuzzy logic and it integrates visual inspection with in situ investigations for carbonation and chloride content. Distress manifestations and repair priorities are classified. Condition is related to repair priorities through condition ratings. Repair priorities are fuzzy in nature as they are dependent on interpretation of the inspector. Questionnaire survey is prepared and responses are collected from the experts. Obtained data are used for development of fuzzy membership functions for defined repair priorities. A building can be subdivided into various elements. Observations for various distress manifestations are recorded for each element, using the format proposed. These observations are combined using fuzzy extension technique to obtain individual membership function for each element. Defuzzyfication using center of sum method provides with the combined building condition index (BCI) from elemental membership functions. Obtained BCI provides direct measure of condition and repair needs of the building. Developed methodology is explained through a case study on condition assessment of an academic building.

In the context of performance-based approaches, sustainability and whole life costing, the concrete structure durability issue has recently gained considerable attention. The present paper deals with service life assessment using durability limit states specialized for concrete structures. Both initiation and propagation periods of reinforcement corrosion are considered and a comprehensive choice of limit states is provided. The approach is based on degradation modeling and probabilistic assessment, enabling the evaluation of service life and the relevant reliability level, serving thus to facilitate the effective decision making of designers and clients. For this purpose the selected analytical models for degradation assessment are randomized and appropriate software has been developed. Three numerical examples are presented: a comparison of modeled carbonation depth with in situ measurements on a cooling tower, and analyses of crack initiation due to corrosion and loss of reinforcement cross section.

Current Bridge Health Index (BHI) in Pontis Bridge Management System applied to assess the bridge health conditions for 615 bridges in city and county of Denver (CCD) does not provide CCD engineers a valuable analysis of the health condition of its relatively small bridge network. This paper explores both the calculation results and the computing methodology of the current BHI. The BHI was computed for the entire 615 CCD bridge network using the two current cost-based methodologies. Based on the analysis, it was concluded that the current BHI is subjective to a municipality’s often imprecise cost data. This coupled with the methodology of heavily correlating cost with a bridge’s condition reveals potential for modification to meet the needs of the CCD. The results of this study are used as a basis for developing an alternate BHI methodology.

Current bridge health index (BHI) in Pontis bridge management system applied to assess the bridge health conditions for 615 bridges in the city and county of Denver (CCD) does not provide CCD engineers a valuable analysis of the health condition of its relatively small bridge network. Both the calculation results and the computing methodology of the current BHI reveal that it is subjective to a municipality’s often imprecise cost data. This paper focuses on developing an alternate BHI. In order to understand the principle and procedure of the BHI calculation, the element weighting point was developed as a new concept in the analysis. The study concluded that the weighting point should reflect the effect of element damage on bridge health and function instead of a percentage of element value. Based on this conclusion, the current BHI was modified. The Denver BHI, a new diagnostic tool, was developed. It has already been adopted in the Pontis bridge management system of the CCD public works department.

Accurate prediction of bridge condition is essential for the planning of maintenance, repair, and rehabilitation. An examination of the assumptions (for example, maintenance independency) of the existing Markovian model reveals possible limitations in its ability to adequately model the procession of deterioration for these purposes. This study uses statistical analysis to identify significant factors influencing the deterioration and develops an application model for estimating the future condition of bridges. Based on data derived from historical maintenance and inspection of concrete decks in Wisconsin, this study identifies 11 significant factors and develops an artificial neural network (ANN) model to predict associated deterioration. An analysis of the application of ANN finds that it performs well when modeling deck deterioration in terms of pattern classification. The developed model has the capacity to accurately predict the condition of bridge decks and therefore provide pertinent information for maintenance planning and decision making at both the project level and the network level.

The monitoring of five precast, prestressed bridge girders during fabrication and service provided the opportunity to observe changes in camber over time. These camber variations were compared with corresponding strain and temperature measurements. Each of the girders was cast outside during the winter. As a result, the cold ground acted as a heat sink, and a significant temperature gradient existed during curing of each of the instrumented girders. These temperature gradients are believed to have caused the wide range in the short- and long-term cambers. A procedure to calculate the effect that curing temperatures have on girder camber is presented. In addition, the measured camber values are compared with predicted values using the multiplier method, improved multiplier method, and a detailed time-step method. It was found for the long-span girders that the measured camber values were on average within 10% of the predicted values using the detailed time-step method, but ranged from 22% lower to 27% higher for the simpler methods.

Core extraction is the most common method for measuring concrete layer thickness in pavement construction. Although this method provides a very accurate thickness measurement, it is destructive, time-consuming, and does not provide adequate representation of the concrete layer thickness variability. Ground-penetrating radar (GPR) is a nondestructive evaluation technique that has been successfully used in several transportation applications, such as subsurface exploration and condition assessment. The main objective of this research is to investigate the accuracy and cost-effectiveness of using GPR in thickness measurement of concrete pavement for quality assurance purposes. A high-resolution 1.6-MHz ground-coupled antenna was used to perform grid scans and measure concrete thickness for several laboratory and field experiments. Results indicated that the use of metal objects underneath the concrete layer to improve bottom surface reflectivity was necessary for a reliable thickness measurement. Also, the use of calibration cores to determine the actual dielectric properties of the concrete was essential for accurate thickness calculation. An average accuracy of 98.5% was achieved when steel plates were used underneath the concrete layer and two cores were extracted for calibration. The effect of concrete age on GPR thickness measurement accuracy was also investigated.

The objective of this research is to develop and implement a stochastic method that can be applied to characterize random failures in critical infrastructure systems. We particularly focus on blockage failures in sewer systems that are nonmechanistic and result from combination of external factors, including deterioration in condition. The method was implemented using a data set consisting of sewer blockage failure records from a small municipality. Statistical tests were conducted to: (1) ensure that available data set is representative and (2) estimate parameters of distributions that appropriately characterize failure event arrival pattern. Failure trends were also analyzed to identify the influence of local factors and justify the choice of the distributions used to characterize interarrival times. Based on the analysis, we explored the challenges in developing a reliability model across the life cycle of a sewer system. In addition, specific examples were also presented to illustrate how the method can be applied to support system maintenance decisions. The results of this study illustrate how the memoryless property can be assumed in analyzing failure events, while explicitly considering context specific influences. Finally, the methods described in this paper are extensible and can be applied generally to analyzing random failures in other infrastructure systems as well.

This study describes results of surveys with Schmidt hammer conducted after the earthquake of August 15, 2007 in coastal cities of Ica, Pisco, and Chincha, Peru. Statistical analysis included comparison of data on compressive strength collected from various types of buildings in damaged and intact walls and bricks. Results of statistical analysis suggest that architecture and nonstructural building design considerations in masonry structures may be more important determinants of seismic resistance than construction material strength. Comparison of mortar samples with respect to structure ownership revealed that strength of mortar at test locations in privately owned buildings was significantly greater than in public buildings.