In 1991, seven corrosion inhibitors, surface applied liquids and concrete admixtures, were identified as promising for the repair of reinforced concrete structures subject to chloride induced corrosion. Small scale (1 ft.²) reinforced concrete specimens were cast to evaluate the inhibitors effectiveness. A treatment matrix was established to evaluate the inhibitors performance on three ranges of corrosion activity and evaluate the effect of application time and drying. Corrosion rate measurements taken with a linear polarization device were used to monitor the inhibitors effectiveness. The effect of the admixtures on the concrete properties, and the effect of the surface applied inhibitors on the overlay bond strength were evaluated. Rapid freeze-thaw tests were conducted to estimate the durability of the inhibitor modified concrete. Three combinations of inhibitors were identified for large scale testing after ten months of accelerated chloride exposure. The larger specimens, removed from an actual bridge deck, were treated to test the effective inhibitors field application techniques. Service life estimates were made for the two combinations of inhibitors which were most effective to aid the engineer in assessing the inhibitors cost effectiveness. / Master of Science

This research is aimed at investigating and analyzing the rain-windinduced cable vibration phenomena experienced in cables of cable-stayed bridges and also the countermeasures employed by engineers to mitigate the large-amplitude vibration problem reported by various researchers around the world. In order to investigate the problem of the water rivulet creation at the top of the cable surface, a single-degree-of-freedom (SDOF) analytical model was developed and analyzed. This thesis studies the aerodynamic instability of cables in cable-stayed bridges by doing literature review of a typical in-situ test, developing a single degree-of-freedom (SDOF) analytical model, and an ANSYS finite element model. Furthermore, a linear viscous damper that acts as a countermeasure to the large amplitudes of vibration is reported and analyzed. The suppression characteristics and damper effectiveness of such countermeasure are summarized. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

Most existing structural health monitoring (SHM) techniques are based on measured acceleration data. Such practice, however, is highly expensive to operate, mainly due to cumbersome, time-consuming and expensive installation of sensors and their data acquisition systems. As an emerging noncontact method, the vision-based displacement sensor systems have attracted significant research interests and offered a promising alternative to the conventional sensors for SHM. However, most existing vision-based sensors require physical access to the structure to install a predesigned target panel, which has a higher contrast and thus is easier to track. Besides, most studies are carried out in controlled laboratory environments. The accuracy and robustness of vision sensors in the outdoor field conditions have not been fully investigated. It is also noted that current researches are mainly focusing on the measurement performance evaluation of vision sensors, without discussing the use of the measured displacement data for SHM. This dissertation develops a high-precision vision sensor system for remote and real-time measurement of multipoint structural displacements by tracking natural targets on structural surfaces. Two sets of software packages are developed respectively based on two advanced template matching algorithms (i.e., the upsampled cross correlation and the orientation code matching) incorporated with different subpixel techniques. Comprehensive experiments, including laboratory shaking table tests and field bridge tests, are carried out to evaluate its performance. Satisfactory agreements are observed between the displacements measured by the proposed vision sensor and those measured by high-performance reference displacement sensors. Moreover, this study examines the robustness of the vision sensor against ill environmental conditions such as dim light, background image disturbance and partial template occlusion. This dissertation further explores the potentials of the vision sensor for fast and inexpensive SHM applications, by demonstrating the usefulness of the displacement data for experimental modal analysis, finite element (FE) model updating, damage detection, etc. For a three-story frame structure, the modal analysis shows that the obtained natural frequencies and mode shapes from displacement measurements by using one camera match well with those by using four accelerometers. In fact, the vision sensor can achieve smoother mode shapes which would make damage localization more accurate, while the resolution of mode shapes from accelerometers is limited by the sensor number. This has been demonstrated from the damage detection result of beam structures based on the mode shape curvature (MSC) index. To address the needs for monitoring aging railway and highway bridges, coupled train-track-bridge and vehicle-bridge FE models are firstly developed to study the dynamic interactions between bridges and moving trains/vehicles. Subsequently, a time-domain model updating approach for railway bridges is proposed based on the in-situ measurement of the bridges’ dynamic displacement histories by the proposed vision sensor. This dissertation further proposes a bridge damage detection procedure that utilizes vehicle-induced displacement response and the MSC index without requiring prior knowledge about the traffic excitation.

Bridges in the US are severely damaged or suffer collapse from fires at significant rates, even when compared to other hazards such as earthquakes. Fire-induced bridge collapses are perpetuated by the general lack of installed fire protection systems. Therefore, new materials and applications are needed to mitigate structural damage that can be caused to civil infrastructure by severe fires. Accordingly, the objective of this study is to further the development of new fire protection applications in transportation structures. Specifically, the investigation centers on the development of new applications in passive fire protection materials, within the context of shielding steel-girder bridges against severe fire effects. A steel-girder bridge has been selected for study, and a high-resolution finite element model has been formed based on the corresponding bridge structural drawings. Temperature-dependent structural material properties and thermal properties have been synthesized and incorporated into the model. Additionally, a representative fire scenario has been formed (in part) based on a recent fire incident that occurred at the selected bridge site. The fire scenario also incorporates the characteristics of a fully loaded gasoline tank truck fire, where a means of incorporating the severe fire into the finite element model (as thermal loading) has been identified and enacted. Coupled thermal-mechanical finite element analyses have been carried out using the (unprotected) steel-girder bridge model. An additional finite element simulation has been carried out, where the steel-girder bridge model has been fitted with a refractory cement material that insulates the underside of the bridge spans. Also, a finite element simulation has been carried out where the steel-girder bridge model has been fitted with intumescent coating material as insulation against fire effects. Both the refractory cement and the intumescent coating materials have been found to possess robust insulation characteristics from the simulation results. Namely, the finite element analysis results indicate that, in the event of a bridge fire, both materials are capable of preventing the buildup of damaging temperatures in underlying structural members. Accordingly, the refractory cement and intumescent coating materials have been identified as successful passive fire protection materials for the fire scenario and bridge case considered.

This thesis examines the stress relaxation phenomenon that may occur in stainless steel rods that are used as part of an all-stainless steel externally post-tensioned rod system for strengthening reinforced concrete pier caps in shear. An overview of the stress relaxation phenomenon and its modeling is presented. Previous work on stress relaxation of stainless steel is reviewed and used to select an appropriate stress relaxation model to analyze the stress relaxation data obtained from experiments performed during this research. An experimental program utilizing six specimens of Type 304/304L stainless steel stainless steel rods similar to those likely to be candidates for pier cap rehabilitation is presented, and the data are analyzed using the model identified from the review. This model reasonably captures the behavior of the resulting stress relaxation with time, and calculates stress values that are fairly close to those obtained experimentally. Using this model to predict long-term stress losses in a service environment, guidelines for design and installation of the post-tensioned stainless steel rods are proposed.

A number of older bridges built before the 1970’s were constructed with floor systems consisting of a non-composite concrete slab over steel girders. Many of these bridges do not satisfy current load requirements and may require replacement or strengthening. A potentially economical means of strengthening these floor systems is to connect the existing concrete slab and steel girders to permit the development of composite action. This dissertation describes a research program investigating methods to develop composite action in existing non-composite floor systems by the use of postinstalled shear connectors. Three types of post-installed shear connection methods were investigated. These methods are referred to as the double-nut bolt, the high tension friction grip bolt, and the adhesive anchor. These post-installed shear connectors were tested under static and fatigue loading, and design equations for ultimate strength and fatigue strength were developed. These post-installed shear connectors showed significantly higher fatigue strength than conventional welded shear studs widely used for new construction. The superior fatigue strength of these post-installed shear connectors enables strengthening of existing bridge girders using partial composite design, thereby requiring significantly fewer shear connectors than possible with conventional welded shear studs. Five full-scale non-composite beams were constructed and four of these were retrofitted with post-installed shear connectors and tested under static load. The retrofitted composite beams were designed as partially composite with a 30-percent shear connection ratio. A non-composite beam was also tested as a baseline specimen. Test results of the full-scale composite beams showed that the strength and stiffness of existing non-composite bridge girders can be increased significantly. Further, excellent ductility of the strengthened partially composite girders was achieved by placing the postinstalled shear connectors near zero moment regions to reduce slip at the steel-concrete interface. Parametric studies using the finite element program ABAQUS were also conducted to investigate the effects of beam depth, span length, and shear connection ratio on the system behavior of strengthened partially composite beams. The studies showed that current simplified design approaches commonly used for partially composite beams in buildings provide good predictions of the strength and stiffness of partially composite bridge girders constructed using post-installed shear connectors. / text

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 115-117) / Highway bridges are exposed to numerous elemental and loading issues that are extremely difficult for a designer to anticipate and account for during design. The current state of practice is to design a bridge deck for a certain life span and then turn the bridge over to maintenance personnel who attempt to prolong the life of the deck through a variety of repair and rehabilitation measures. These repair measures are rarely, if ever, considered during the design process of the bridge deck. Numerous researchers have looked at making bridges, specifically decks, more repairable. The majority of these research efforts have focused on the bridge deck system as a whole. Other researchers have looked at individual elements of the bridge deck to girder connection to see if the required strength could be achieved while making the connections easier to take apart. One of the main components in the bridge deck to girder system is the steel shear stud connection, which is used to create composite action between the deck and the girder. Numerous researchers have studied this connection from a strength perspective, and the strength equations for the shear connection have been codified. Shear connections using headless studs have been researched as well, but always as a part of a larger deck to girder connection system. The headless stud has never been researched to see how it responds to a shear loading. This study looks at headless studs with varying levels of debonding along the stud shaft to analyze the impact on the load resistance that the levels of debonding would have. Granular materials for the shear transfer of load are also looked at. The results show that, as expected, the headless, debonded shear studs can carry less load than a bonded stud, but the difference in load carrying capacity is within the suggested over-estimation range of the codes that other researchers have suggested. These results suggest that the use of headless, debonded shear studs in a deck to girder connection is a feasible way to make that connection more repairable. / Funded by the U.S. Dept. of the Army. / by Berndt F. Spittka / S.M.

李嘉寶. / "2007年8月". / 論文(哲學碩士)--香港中文大學, 2007. / 參考文獻(leaves 121-129). / "2007 nian 8 yue". / Abstract also in English. / Li Jiabao. / Lun wen (zhe xue shuo shi)--Xianggang Zhong wen da xue, 2007. / Can kao wen xian (leaves 121-129). / 緒論 / Chapter 1. --- 前言 --- p.1 / Chapter 2. --- 硏究回顧 --- p.3 / Chapter 3. --- 論文寫作框架 --- p.13 / Chapter 第一章 --- 修橋補路一一明清時期的慈善、國家與社會 / Chapter 1. --- 前言 --- p.15 / Chapter 2. --- 蘇松地區的修橋統計 --- p.18 / Chapter 3. --- 矛盾的修橋者一一有責無錢的官員 --- p.22 / Chapter 4. --- 慈善的修橋者一一行善積德的士紳 --- p.33 / Chapter 5. --- 修橋補路的中介者一一善堂的興起 --- p.42 / Chapter 6. --- 小結一一從修橋補路看國家與社會關係 --- p.45 / Chapter 第二章 --- 上海地方自治與路政發展 / Chapter 1. --- 前言 --- p.47 / Chapter 2. --- 兩種制度的相遇一一南市路政的起步 --- p.49 / Chapter 3. --- 自治十年的路政發展 --- p.58 / Chapter 4. --- 路政的經濟基礎 --- p.70 / Chapter 5. --- 小結 --- p.75 / Chapter 第三章 --- 自治與社會 / Chapter 1. --- 前言 --- p.76 / Chapter 2. --- 從慈善到路政之過渡 --- p.77 / Chapter 3. --- 自治組織的權威危機與加強 --- p.85 / Chapter 4. --- 小結 --- p.95 / Chapter 第四章 --- 自治與國家 / Chapter 1. --- 前言 --- p.96 / Chapter 2. --- 城濠公地案中自治組織與地方政府的關係 --- p.97 / Chapter 3. --- 拆城築路案中自治組織與地方政府的關係 --- p.101 / Chapter 4. --- 兩案之結局 --- p.109 / Chapter 5. --- 小結 --- p.115 / 結論 --- p.117 / 參考書目 --- p.121

The Astoria-Megler Bridge is a 6.6 kilometer (4.1 mile) long bridge, connecting Oregon and Washington on US 101, with a continuous steel truss main span of 376 m (1232 ft). It is the second longest main span bridge of this type in the world. Due to vortex shedding, some of the long truss verticals exhibit wind-induced torsional vibrations. These vibrations can create large numbers of repeated stress cycles in the truss verticals and the gusset plate assemblies. The members and connections were not designed for such conditions and the impact of this behavior on the service life of the bridge is uncertain. A full-scale representation of one of the truss verticals observed to exhibit such wind induced torsional response was fabricated and tested in the Structural Engineering Research Laboratory at Oregon State University. Experimental data of the rotational behavior and the stress distribution along the vertical were collected using inclinometers, an angular rate sensor, and uniaxial and rosette strain gages. The data collected were compared with existing analytical methods and predictions from finite element models. The observed experimental results including twist angle, stress distribution, and stress magnitude were well captured by both the finite element model and the analytical equations. Using analytical expressions, the fatigue lives of the existing bridge verticals were predicted based on assumed storm duration and recurrence. / Graduation date: 2013