Journal of Performance of Constructed Facilities

Exponent Failure Analysis Associates was retained by a municipal government to perform an independent study of a fatal collapse in a local sewer treatment plant. The reinforced concrete dome shell covering a cylindrical prestressed concrete digester tank collapsed due to sludge overfilling. The collapsed dome, similar to domes on two adjacent identical tanks, showed radial and circumferential cracking prior to the collapse. Analysis showed the dome cracks were a result of temperature and shrinkage stresses, and of internal overpressure happening at some time prior to the overpressure resulting in the collapse. Inspections of the postfailure debris and analysis of the dome cracking preceding the collapse show practically no relationship between the dome condition prior to collapse and the failure. Failure of the sludge level monitoring system and the lack of a sludge overflow system are cited as the primary reasons for the failure.

The engineering assessment of fire damage to a concrete slab provided the opportunity to compare the results of in situ, nondestructive evaluation (NDE) techniques and laboratory testing of specimens taken from cores extracted from the fire damaged slab. This paper discusses and compares results of in situ pulse velocity and impact-echo testing with dynamic elastic modulus and air permeability index test results of $25\mathrm{mm}$ $\left(1\mathrm{in.}\right)$ thick disks sawed from concrete cores removed from selected areas of the damaged slab. Both the NDE techniques and the laboratory testing of thin disks identified the presence of damage as a result of the fire. Analysis of the relatively thin concrete specimens permitted assessment of the presence and degree of damage in thin layers, and provided important and useful data on concrete properties for engineering assessment which was not available from NDE alone. Compressive strength results were consistent with the results of other tests but largely inconclusive by themselves. Impact-echo testing was able to identify the presence of a severely deteriorated concrete layer but could not identify the extent or depth of damage or clearly identify less damaged areas. A distressed layer of concrete was found by subsequent laboratory testing to be limited to a near-surface zone in some areas as suggested by the pulse velocity evaluation, but pulse velocity based analysis resulted in an overestimate of the depth of the damage. The findings highlighted a shortcoming of using conventional strength testing alone on investigations involving relatively thin layers of damage and pointed out several key limitations in the use and interpretation of nondestructive evaluation and associated analysis in a field assessment project.

Practitioners were invited to respond to a problem statement published in the November 2000 issue of the Journal of the Performance of Constructed Facilities asking for an estimate of the compressive strength of in situ concrete based on hypothetical results of compressive tests on ten cores. Responses were received from 23 persons. Several respondents provided more than one estimate. It was found that there were wide variations in practice for determination of compressive strength from cores. Estimates varied from $\mathrm{3,000}\text{to}\mathrm{5,000}\mathrm{psi}$ . The most frequent estimate was $\mathrm{4,000}\mathrm{psi}$ . The paper presents background information on code provisions relating to core testing, summarizes and discusses the responses, and offers observations based on the responses regarding investigations where compressive strength of concrete in an existing structure is determined from test of cores.

A soil reinforcement system using the combination of glass-fiber-reinforced polymer (GFRP) pipe and pressure grouting has been developed by a Korean company. The system is being adopted as slope stabilization measures in Hong Kong. Individual GFRP pipes were designed and installed as soil nails with the exception that two-stage pressure grouting was applied instead of gravity grouting. A full-scale field evaluation on constructability and in situ performance of the system was performed in Hong Kong. The performance of the constructed nails was evaluated by pullout tests. The construction procedure, site adaptations of the Korean product made in Hong Kong, field test procedure, and performance of the constructed soil nails are reported in this paper.

The dynamic performance of a woodframe structure is examined through the qualitative correlation between the transient interstory drift and the observed damage following a series of full-scale shake-table tests. The structure was subjected to simulated Northridge earthquake ground motions scaled to seismic hazard levels of 50, 10, 2, and 1% exceedance in 50 years. Added mass was used in an effort to examine the qualitative correlation of the observed performance with the performance tabulated in FEMA 2000. The structure was repaired to the extent possible between each test. The structure was tested at three different structural/nonstructural stages: (1) oriented strand board (OSB) only; (2) gypsum wall board (GWB) and OSB; and (3) OSB, GWB, and a nonstructural interior partition wall, in order to determine the effect of each component and to qualitatively determine its effect on overall damage to the system. It was determined that qualitative damage descriptions were not significantly different from those given in FEMA 2000. It was also found that the percent torsion increased with increasing peak ground acceleration. The effect of GWB on structural response and damage was as expected, but the partition wall behaved differently than expected. Specifically, the partition wall sustained very little damage even though it had full load transfer at the top plate.

State highway officials are often put in situations that require them to make difficult decisions, some literally involve life or death. Among these are decisions dealing with bridges that may have structural, scour, or seismic problems. This paper proposes a risk index $\left(R\right)$ that assesses risk and prioritizes bridges with unknown foundations. Primary risk parameters and their factors for bridges with unknown foundations were identified and analyzed, and a model for calculating $R$ was designed. Data were collected for ten bridges from Florida, Indiana, and New York for use in case studies. Two application methods for the model were used to assess $R$ : (1) the abstract model; and (2) the detailed model). Courses of action based on $R$ are discussed for various bridges. The model was validated using a holistic evaluation method, which proved to be robust in risk assessment. Although this paper is written to assist bridge managers in assessing risk and prioritizing activities, the research results shared in this paper are relevant to both researchers and practitioners. The paper provides practitioners with a tool for evaluating and ranking their bridges based on risk and provides researchers with risk parameters and factors, a model to evaluate this risk, and a methodology of quantifying the qualitative effect of subjective factors.

The MD 24 Bridge over Deer Creek in Harford County, Md., was one of the projects chosen by the Federal Highway Administration’s Innovative Bridge Research and Construction Program for bridge deck replacement by fiber-reinforced polymer (FRP) composites. A thorough discussion is presented on Maryland State Highway Administration’s first bridge rehabilitation project utilizing a FRP deck. The discussion includes design details, installation procedure, construction methods and in situ load testing with a wireless monitoring system. The research team installed a monitoring system to record the effects of live loads on the bridge system, including truss members, steel stringers, and plate action of the FRP deck. Finite-element models were also used in this phase. Dynamic effects of the FRP system, composite action between steel stringers and the FRP deck as well as the effective width and distribution factors of stringers were obtained and compared with the AASHTO specifications. Recommendations are also offered on improving the design details based on this experience.

As buildings have become larger and house more people, political and societal issues have become more complex, and risks associated with occupying buildings have changed. In particular, since the terrorist attacks of 2001, the anxiety levels and perceived risks of building occupants (especially occupants of tall, high-profile buildings) have increased. These perceived risks include risks of terrorist attacks, natural disasters, the possibility of bomb threats, and catastrophic fires. The public’s perception of risk is already incorporated into building design codes and performance-based design (PBD) methods for such hazards as earthquakes and fires—explicitly in some cases, implicitly in others. Risk perception will clearly need to be addressed in the design of buildings, as trade-offs in “acceptable” risk versus cost must be made. As terrorism represents a constantly changing design challenge, and is a target-specific hazard, as opposed to a location-specific hazard, it seems unlikely that prescriptive code requirements will be entirely effective at addressing this hazard. PBD codes are a promising approach for design issues that deal with such “cutting-edge” concepts.

Lack of proper pavement base and subgrade compaction leads to premature failures that account for millions of dollars in damages. Controlled low-strength material (CLSM) concrete was introduced in this study as pavement base material near a manhole where proper compaction is unachievable. Rut-resistant stone matrix asphalt was placed on top of the CLSM as a wearing surface layer. Dynamic cone penetrometer (DCP) testing was used to monitor CLSM construction. One day after placing, the CLSM gained sufficient strength to support construction traffic. Further, DCP results indicated that the CLSM possessed uniform characteristics of concrete that could improve the load-bearing capacity and serviceability of the pavement near the manhole. After 18 months of heavy truck traffic, maximum rutting was $5\mathrm{mm}$ , well below the failure criteria of $12.5\mathrm{mm}$ . Based on cost and performance, CLSM concrete has the potential to improve problematic areas in pavement.

Developed in the early 1990s, ultrathin whitetopping (UTW) is a relatively new technique for asphalt pavement rehabilitation. To evaluate the applicability of UTW pavement in Florida, in 1997, the Florida Department of Transportation (FDOT) constructed an experimental UTW pavement in a weigh station along I-10, located in north Florida. The performance of these test sections, however, was less than ideal, with the observation of some early cracking on the concrete surface, which developed into severe cracking with time. Therefore, a forensic investigation was conducted to determine the causes of the problems in these UTW sections, so that lessons could be learned from this experimental project, the use of UTW under Florida’s conditions could be adequately assessed, and UTW technology could be properly applied in the future. The scope of work consisted of field evaluation, laboratory testing, and pavement design evaluation. Field evaluation included a pavement condition survey, pavement temperature measurement, nondestructive load testing using a falling weight deflectometer, and slab thickness determination. Laboratory tests were performed to determine concrete and asphalt material properties. Other design and traffic data were also acquired from FDOT. Data collected from the field evaluation and laboratory testing were used in conjunction with a mechanistic UTW pavement design/evaluation procedure to determine the possible causes for premature failure. From this comprehensive evaluation, the primary cause for the failure was found to be inadequate UTW pavement design. The inadequacy of the combination of thickness and slab dimensions contributed to the early cracking of the UTW pavement.