Journal of Performance of Constructed Facilities

Slender floor structures are becoming increasingly prone to excessive vibration due to human-induced walking excitation. To prevent discomfort of floor occupants and/or malfunctioning of sensitive equipment, it is necessary to have a reliable means of estimating floor vibration in the design phase. For accurate estimation of the floor vibration, both reliable excitation and structural models are required. This paper concentrates on the former by evaluating the performance of the existing force models and suggesting their improvement. For this a force model adopted in the United Kingdom by the Concrete Society was applied to four nominally identical floors using their experimentally identified modal properties. After comparison with experimental data the drawbacks of the force model were identified after which an improved model of the walking-induced dynamic force, based on the combination of two existing methodologies used separately for low- and high-frequency floors, is proposed. The improved model accounts for the intersubject variability in the walking force with respect to the pacing frequency, step length, and forcing magnitude. Moreover, it includes all relevant frequency components of the walking force into analysis, removing the need for classification of floors as low or high frequency. The proposed approach should help designers and building owners to make more informed decisions when evaluating vibration serviceability of floor structures.

Despite the great progress made in the last few years in the manufacturing of ceramic bricks and their fitting technology, brick façades still suffer from a series of critical problems and in some cases the number of pathologies have even increased. The most common and critical problem of brick façade enclosures is the detachment of pieces from the die, thus the loss of union. This detachment can be associated with three different causes: an inadequate prescription of the griping material, the absence of control joints to make the enclosure compatible, and the incidence of sun and rain on the façades. While the first two factors are directly related to the design process, the fitting techniques, training of the work force, and quality control efficiency, the third factor is related to environmental factors that generate a different microclimate in each façade depending on its orientation. This paper describes some examples of detachments in brick façade enclosures and the main causes that originated from them.

A significant number of accidents has occurred with demountable grandstands in the past as well as recently. The performance of such structures is the subject of this paper. First, structural details and some structural systems of actual grandstands are presented and discussed. Next, specifics of the design, erection, and inspection process are detailed. Finally, a survey of cases of collapse of demountable grandstands is presented and discussed. Ninety three cases of collapse were found between the years 1889 and 2008, in which more than 85 people died and 6,350 were injured. From these, 35 cases in which information about the causes of collapse were available were selected. An analysis of the causes showed that unexpected or excessive loads were the major contributing cause, followed by problems with the supports, connections, and bracing. Possible measures that could be adopted aimed at minimizing the risk of accidents with these structures are discussed.

This case study illustrates the investigation and remediation of distress and subsidence on a multilevel, posttension, cast-in-place concrete parking garage that was constructed at the crest and over the side of a gentle sloping hillside. A comprehensive exploration program was conducted to determine the cause of the subsidence. The investigation included core borings through the distressed caissons and the underlying bedrock and the use of a downhole camera to determine the rock conditions. Based on the investigation, it was concluded that the caisson subsidence was caused by the collapse of a large cavity underlying the sandstone. A grouting program was performed to reduce the potential of further settlement. This paper summarizes the findings and conclusions derived from this investigation and the remedial measures undertaken to reduce the potential of further distress to the structure.

Seasonal temperature displacements are an important component of the total displacements recorded by pendulum measurements at gravity dams located in northern regions. A hybrid dam displacement model is presented in this paper to interpret these displacements and extrapolate the response for an extreme thermal event not yet experienced by the dam. The hybrid model uses a simplified deterministic structural dam representation with beam elements in complement to a hydrostatic seasonal time (HST) statistical displacement model. Comparisons are first established between 1D heat transfer analyses of typical gravity dam sections, and 2D finite-element (FE) analyses. Thermomechanical displacements are compared to show the validity of the proposed simplified deterministic beam model for typical dams. A case study of an actual $40\mathrm{m}$ gravity dam located in Quebec, Canada is then presented. It is shown that the deterministic model can be calibrated using the pendulum displacements and the HST model. The calibrated deterministic model is then used to extrapolate the displacement response for extreme thermal events not yet experienced by the dam. The proposed methodology represents a simple extension of the gravity method, widely used to verify gravity dam stability, as a first step to interpret recorded pendulum displacements and set appropriate warning and alarm levels on a rational basis before developing 2D and 3D thermomechanical FE deterministic dam models that require a lot of resources and expertise to be used effectively.

Where faulting takes place due to the absence of dowel bars and inadequate subbase support in jointed concrete pavement (JCP), dowel bar retrofit (DBR) is used to improve load transfer efficiency (LTE) and to prevent further faulting of slabs at transverse joints. Even though DBR generally improves LTEs and overall performance of JCPs, not all DBR projects have been successful. Faulting reoccurred within $2\text{years}$ after DBR treatment on US59 in Texas. An investigation from the cores taken in the project revealed excessive voids under a dowel bar due to poor consolidation of the grouting material. A laboratory investigation was performed to determine the most critical factors for adequate consolidation of grouting materials in DBR. Typical rapid-setting grout materials widely used in DBR were selected and full-scale specimens were made for evaluations. Four testing variables for consolidation performance were investigated: time of placement after mixing, vibration time, slot width, and maximum aggregate size. Maximum aggregate size and slot width were not critical factors for consolidation performance of grout. The most significant factor was vibration time. Twenty s of vibration is recommended. Placement time was also an important factor, with grout materials placed after initial set performing poorly. Delayed placement of grout materials without vibration led to the most voids under the dowel bars.

Dynamic response of a bridge under traffic load induces acoustic energy at the bridge surface. The acoustic energy change generates an additional coupled noise component caused by vibration of a bridge deck associated with the pavement conditions and moving velocity of the vehicle. This paper presents a three-dimensional finite-element method developed for the dynamic response and noise propagation model, and analyzes the coupled effect induced by traffic loading based on different pavement conditions. Even though vibration-induced noise at the bridge is below the audible frequency range of $20–\mathrm{20,000}\mathrm{Hz}$ , it amplifies the traffic noise source to the highly annoyed level of noise in the metropolitan area. Among several factors that contribute to the traffic noise, interaction between pavement and vehicle is considered according to the different surface roughness and vehicle velocity. The result shows that poor pavement condition contributes to the increase of traffic noise at a high traveling speed of the vehicle. In the pavement maintenance stage, the coupled effect as an additional noise source should be considered to mitigate the traffic noise for its added value in conjunction with regulation of engine emission noise and construction of a noise barrier.

This paper presents a comprehensive overview of recent developments in the performance evaluation and flexural response of existing bridges from fundamental concepts to advanced topics. The focus is particularly on the structural evaluation to enhance the quality assessment of constructed bridge superstructures, taking into account a synthesis of the most important contributions to the flexural behavior of existing bridges, such as dynamic responses and lateral load distributions. This state-of-the-art paper provides a critical review of published literature and existing assessment methodologies in conjunction with corresponding analysis techniques, including technical comments on the code provisions. Detailed descriptions of the important parameters influencing flexural responses of existing bridges are discussed, such as the geometric effect, loading configuration, present condition of a bridge, and contribution of secondary structural elements. The review also includes the investigation methodologies, namely, the diagnostic and proof load tests. Finally, the current research needs to further advance the performance evaluation technologies for existing bridge superstructures are recommended.