Journal of Performance of Constructed Facilities

A floor supported on long-span beams, which was designed to accommodate bio research instruments, is evaluated for vibration induced by people walking. First, a brief review in vibration criteria is given. The variation of force time histories imposed by people’s feet on supporting objects is also discussed. Both beam and floor finite-element models are then used to simulate the local walking response of the floor mathematically. Footfall forces are applied to the finite-element models via triangular distribution function. A comparison of the time history analysis results with the vibration criteria shows that the floor performs well under people walking. Field measurements were also conducted after the completion of the construction. The measured results show a good correlation with the finite-element analysis results. During the analyses, it was also found that as long as the local floor model covers a structural bay, the boundary conditions of the floor model do not affect the response much. Using an equivalent constant footfall force function can produce similar results compared with those obtained using a more sophisticated force function.

This paper first describes the current state of analysis for the response of unreinforced concrete masonry walls subjected to lateral uniform pressure. The formulation is based on the initial elastic response, the subsequent initiation of cracks and the nonlinear rocking response, and the eventual large displacement and potential collapse. The necessary equations are developed for these phases in the form of a resistance function. The paper then incorporates membrane retrofit materials to strengthen the wall’s resistance to lateral pressure, and develops the necessary resistance function equations. In blast tests, membrane retrofit unreinforced masonry walls have experienced severe cracking and large displacements without collapse. This is of high interest to the Department of Defense, the protection of diplomatic facilities, and the construction industry impacted by hurricanes and other high wind events. The paper concludes with examples that demonstrate application of membrane retrofits indeed increase the resistance of the wall to lateral pressure.

After only 2 months in service, the frontage road of US 290 developed a series of depressions that caused a very poor ride. The main cause of the premature failure was attributed to disintegration of the cement treated base (CTB) layer. This was attributed to two primary factors: (1) a very coarse gradation of the aggregate used in the CTB layer which produced a mix that was prone to segregation during placement; and (2) the CTB layer was placed in two lifts, which were not well bonded together. Another contributing factor was the lack of bond between the CTB and the hot mix asphalt (HMA) surface layer. Secondary factors include high air voids in the HMA layer and low HMA layer thickness. The material, when prepared carefully in the lab at the design cement content, passed the strength requirement of $2.07\mathrm{MPa}$ . But this coarse mix appears to have been difficult to place correctly in the field. The coarsely graded aggregate used on this project appears to be prone to segregation, either during placement or compaction. The ground penetration radar results (with confirmation by core samples) indicated that most of the problems were at the bottom of the upper CTB lift. The CTB was placed in two lifts and very poor condition was found between the two CTB layers. This problem was coupled with a thin, porous, and poorly bonded HMA layer that permitted moisture to enter the CTB layer. Similar failures have also been reported recently on other CTB projects in Houston.

This study investigated the influence of several construction practices on the bond strength at the interface between pavement layers. These practices included the surface treatment, curing time, residual application rate, and equipment tracking. Three tests were performed for estimating the bond strength between an existing hot mix asphalt (HMA) and a newly constructed HMA overlay, namely the Florida Dept. of Transportation shear tester, the University of Texas at El Paso pull off test, and the torque bond test. Testing involved a CSS-1 type emulsion as the tack coat. The results from the three tests were statistically analyzed. Generally, milling provided a significantly better bond at the interface between the existing surface and the new overlay. Curing time had a minimal effect on the bond strength. The results indicated that the absence of tack coat did not significantly affect the bond strength at the interface for the milled sections, whereas it severely decreased the strength for the nonmilled sections. The results also showed that increasing the residual rate of tack coat did not generally affect the bond strength at the interface.

In Texas, many miles of plain jointed concrete pavement (JCP) were constructed without proper load transfer devices such as dowels. After a number of years of service, some JCP sections without dowels showed distresses in the form of faulting at transverse joints. Some of the sections were designed in accordance with the AASHTO 1986 Guide, which required $50–75\mathrm{mm}$ thicker slabs in exchange for not using dowels. This pavement design did not work, with faulting at transverse joints that cause poor ride. Dowel bar retrofit (DBR) was performed on four projects to restore the pavement condition. Overall, DBR restored load transfer efficiency and resulted in improvement of ride quality. Even where the subbase stiffness is 5–10 times less than the minimum value required for proper performance of JCPs, properly installed DBR effectively restored pavement condition with minimum faulting after decades of service. Therefore, it indicated that DBR is able to minimize the faulting even where there is poor base/subgrade support. This is significant in that there are no effective and practical methods to improve subbase conditions in existing concrete pavement, whereas DBR can restore pavement conditions at a reasonable cost. However, not all DBR projects were successful. In one DBR project, faulting in the range of $6.4–9.5\mathrm{mm}$ occurred after less than 2 years of treatment. Forensic investigation revealed voids under the dowel bars, which indicates poor consolidation of the grout material. Efforts are currently underway in TxDOT to improve specifications for grout materials and DBR construction.

The objective of this study is to provide a simple methodology to conduct preliminary seismic assessment and ranking of bridge embankments in order to identify and prioritize embankments that are susceptible to failure. A ranking model that provides a priority list of embankments with the highest seismic risk of failure is generated. A step-by-step methodology is presented in a flowchart to estimate the seismic slope stability capacity/demand ratio, displacement, and liquefaction potential of bridge embankments. Three categories are presented to identify the failure risk of the embankments. The ranking model is useful for a quick sensitivity assessment of the effect of various site conditions, earthquake magnitudes, and site geometry on possible movement of designated embankments. The priority list will enable decision makers to decide on either carrying out further detailed evaluation or consider other appropriate actions for the bridge embankments with the highest seismic failure risk.

Soil types and depth of bedrock are not available for the majority of bridge embankments to allow detailed seismic analysis and risk assessment. The accompanying paper provides a quick methodology for preliminary seismic risk assessment, ranking, and prioritization of bridge embankments along priority routes. The objective of this paper is to apply the methodology to identify the seismic risk of 127 bridge embankments along I-24 in western Kentucky. The variables of each embankment including the geometry, type and properties of underlying soil, elevation of the natural ground line, and level of bedrock are estimated. The seismic slope stability capacity/demand ratio, displacement, and liquefaction potential of each bridge embankment are calculated. Three categories are presented to identify the failure risk of the embankments. A priority list of the embankments with the highest seismic risk of failure is generated for I-24 bridge embankments in western Kentucky during designated seismic events. The priority list will enable decision makers to decide on either carrying out further detailed evaluation or considering other appropriate actions for the embankments with the highest failure risk.

The collapse of a suspended soffit consisting of portland cement plaster stucco on metal lath was investigated to determine the probable cause of collapse after over 30 years of service. Soffits of this type are often constructed with minimal, if any, details provided by the project architect or engineer. Without design guidance, the builder usually relies on typical industry practices and prior experience to construct these soffits. While experience may result in a safe installation in many instances, long-term performance without distress is no guarantee that no defects exist.