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An important role of postearthquake emergency management is to minimize the restoration time, which is the sum of the travel time and the response time. The travel time is the time needed to reach the affected area from the dispatch location, whereas the response time is the time required to bring the situation under control after reaching the affected area. A number of built environment variables, e.g., building collapse probability, and natural variables, e.g., flooding probability, are known to affect the restoration time. Data from St. Louis, MO, USA, are used in conjunction with a discrete-event-based simulation model to identify the statistically significant variables via an analysis of variance. The experimental results show that in order to reduce the loss of life, the volume of resources and the building collapse and flooding probabilities are significant factors that should be accounted for in the emergency-response planning for an earthquake. [ABSTRACT FROM AUTHOR]

Emergency responders are typically notified immediately after a major earthquake strikes. However, a time delay, called the travel time, is usually experienced between the notification and the arrival of the responders on the scene. The reparative work necessary after the responders arrive takes an additional amount of time, called the response time, depending on the nature of the damage and the volume of resources available. In a smart city, the restoration time, which is the sum of the travel and response times, should be minimized. A new discrete-event-based simulation (DEBS) model is presented in this paper to estimate the restoration time needed to bring the situation under control after notifying the response center. The DEBS model not only relaxes restrictive assumptions on travel time made by the Markov chain models from the existing literature, but it can also quantify the impact of resource volumes on restoration times. Additionally, the DEBS model is very useful for training purposes. The DEBS model was employed on a case study from the state of Missouri (U.S.). The experiments demonstrate that numerical results with the model take a short amount of computational time and that it can be implemented on a real-time basis in a smart-city infrastructure. [ABSTRACT FROM AUTHOR]

With the depletion of natural resources and the growing awareness of environmental protection, it is increasingly important to apply more renewable resources in construction material. Considering the low-cost and abundance of plant fibers, this paper proposes a novel cementitious material called plant fibers reinforced alkali-activated slag cementitious material (PF-AASCM). Specifically, the author investigated the types and features of fibers and how they affect the AASCM properties. On this basis, the influencing factors of the mechanical properties and microstructure of PF-AASCM were determined, and the measures to enhance the compressive and flexural strengths of the PF-AASCM were evaluated one by one. Next, the potential of applying plant fibers as internal enhancements of the AASCM was thoroughly explored. The results show that the PF-AASCM is economically and technically viable for many construction applications. The plant fiber reinforcement can enhance the ultimate strength of the AASCM rapidly (70 % growth in 7d and 120MPa/17,000psi in 28d), resulting in excellent acid resistance and freeze-thaw durability. In addition, the optimal mix ratio is 1:4 wt.% between sodium hydroxide and potassium silicate. Under this ratio, the mechanical properties and microstructural features of the sample will be comparable to those of Portland cement. The compressive strength of single-row-hole sample of wheat straw reinforced AASCM was 10.75MPa at room temperature, equivalent to that of standard concrete sample MU7.5. The compressive strength of such a PF-AASCM decreased linearly with the growth in temperature. After the temperature reached 600 °C, the plant fiber still exerted a certain tensile force on the matrix. By contrast, the polypropylene fiber started to melt down after the temperature increased to 200 ~ 400 °C, causing brittle failure of the matrix. Under the high temperature of 200 ~ 400 °C, the fine steel fiber enhanced the compressive properties of samples, which showed clear plastic deformation. The research results shed new light on reducing pollution and enhancing AASCM ductility. [ABSTRACT FROM AUTHOR]

A portable seismic property analyzer (PSPA) was used to simultaneously acquire both ultrasonic surface wave (PSPA-USW) and impact-echo (PSPA-IE) data at predetermined locations along a section of multi-layered pavement. The pavement consisted of a basal concrete layer (~220 mm), an intervening layer of hot-mix asphalt (~60 mm), and a concrete overlay (~220 mm). The section of multi-layered pavement was cored at multiple PSPA test locations for verification purposes. The conditions of the extracted cores were assessed visually, and the static elastic modulus, as well as the compressional wave velocity of each concrete overlay core, were measured in the laboratory. Results from this study demonstrated that the PSPA-USW tool can be used to evaluate the conditions of concrete overlay, the interlayer (hot-mix asphalt), and their bonding conditions from a qualitative perspective. A good correlation between the static and laboratory dynamic modulus from core specimens of concrete overlay were confirmed based on laboratory testing results. However, the field dynamic modulus of core specimens, based on PSPA-USW tests, was lower than both the static modulus and laboratory dynamic modulus. Furthermore, the PSPAIE tool was not able to estimate the depth of the entire pavement and to various pavement layer interfaces due to the interference of flexural mode vibration. Fortunately, the difference between intact and deteriorated pavement can be qualitatively identified from the amplitude spectrum. More core specimens are needed for further studies in order to verify the performance of both PSPAUSW and PSPA-IE techniques for multi-layered pavement condition assessment. [ABSTRACT FROM AUTHOR]

Repair has become a viable option for restoring the use of earthquake-damaged RC elements, even those that have been severely damaged. To select and design an appropriate repair system for damaged RC bridge columns, it is important that results from previous studies are known. This paper presents a comprehensive summary and review of techniques to repair earthquake-damaged RC bridge columns, as well as numerical methods for analyzing the response of repaired columns. Repair of columns with and without fractured longitudinal reinforcing bars is discussed. Studies are reviewed in terms of the apparent damage, repair technique, and performance of the repair. Advantages and disadvantages associated with each repair technique are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study conducted to understand the behavior and stress-transfer mechanism of fiber-reinforced cementitious matrix (FRCM) composites externally bonded to a concrete substrate for strengthening applications. The FRCM composite was comprised of a polyparaphenylene benzobisoxazole (PBO) fiber net embedded within two layers of polymer-modified cement-based mortar. Single-lap shear tests were conducted on specimens with composite strips bonded to concrete prisms. Parameters that varied were bonded length and width of composite. Additionally, the external coating layer of matrix was omitted on a limited number of specimens to examine the interfacial behavior between fibers and matrix and the role of the matrix in the stress transfer. Strain measurements along the composite bonded length were used to investigate the stress-transfer mechanism. Results suggest that the effective bond length of this composite is within the range of 250 to 330 mm (10 to 13 in.). Unlike with fiber-reinforced polymer (FRP) composites, no width effect was observed in terms of the maximum load. Finally, the stress-transfer mechanism at the matrix-fiber interfaces on either side of the fiber net was found to be unequal. [ABSTRACT FROM AUTHOR]

Although a limited number of studies have been conducted on the use of externally bonded composites for torsional retrofit or strengthening of reinforced concrete (RC) members, very few are available on torsional repair. This paper evaluates a method for repairing severely damaged RC columns subjected to torsional moment using externally bonded carbon fiber-reinforced polymer (CFRP) composites. A half-scale RC column that was previously tested to failure under constant axial load and cyclic torsional moment was repaired with externally bonded CFRP using a rapid methodology. CFRP sheets with fibers oriented in both the transverse and longitudinal directions were applied to restore the strength and ductility of the damaged column to its original condition. This study demonstrates that this method can be used to restore the torsional performance of severely damaged RC columns. Contributions of the transverse and longitudinal CFRP sheets to the torsional resistance are evaluated, and repair design for torsional moment using this method is discussed. [ABSTRACT FROM AUTHOR]

This paper examines the results of experimental research performed to test the hypothesis that the effective depth influences the shear strength of reinforced concrete (RC) beams. The analysis of the experimental results reported in this paper indicates that the observed reduction in shear strength with increasing effective depth was a function of differences in relative behavior at failure largely associated with lack of geometric scale in the cracking behavior. In particular, the flexural cracking, which did not scale with beam size, is shown to have influenced the arch action mechanism of shear transfer by interfering with its development in the larger beams but not in the smaller beams, which in turn influenced the relative shear strength of the specimens tested and the observed size effect in shear. [ABSTRACT FROM AUTHOR]

This paper describes the results of numerical simulations performed to investigate the spalling mechanism observed in several partial-depth precast prestressed concrete (PPC) bridge decks. Corrosion-induced cracking of prestressed steel reinforcement and panel butting were modeled using 2D finite element analysis to examine the nature of crack propagation that triggers the spalling effect observed. A parametric study was carried out on the basis of field observations from several bridges. FEM results showed that spalling is sensitive to side and bottom cover, and spacing of reinforcement attributable to bridging cracks. Findings indicate that the spalling mechanism is triggered by the presence of a critical bridging crack. [ABSTRACT FROM AUTHOR]

Laboratory tests of reinforced concrete beams without shear reinforcement have shown that the shear strength (in terms of average shear stress) decreases as the size (depth) of the member increases. This paper discusses the results of experimental research performed to test the hypothesis that the effective depth influences the shear strength of reinforced concrete flexural members that do not contain web reinforcement in the range of overall depth between 12 to 36 in. (610 to 900 mm) where ACI 318-08 does not require skin reinforcement. The results of tests on eight simply supported reinforced concrete beams without shear and skin reinforcement are described, discussed, and correlated herein. The longitudinal reinforcement ratio was approximately 1.25%. The target concrete compressive strength was 10,000 psi (70 MPa). The beam width varied between 8 and 24 in. (203 and 610 mm). All of the beams were simply supported and monotonically loaded in increments at midspan up to destruction. The shear span-depth ratio was maintained at 3.0. Test results show a reduction in shear strength with increasing effective depth; however, significant differences in behavior were observed between the 12 in. (305 mm) specimens and the larger specimens in terms of the amount of flexural cracking, crack progression, load-displacement, and load-strain measurements despite holding other traditionally considered influential parameters constant. These differences suggest that the reduction in shear strength was influenced not only by a size effect but also by differences in behavior and mode of shear transfer at failure (beam action versus arch action). For the beams tested in this study, flexural crack spacing did not scale with beam size. The change in ACI 318-08 restricting isolated beams without minimum shear reinforcement to heights not greater than 10 in. (250 mm) is supported by the findings of this study. [ABSTRACT FROM AUTHOR]

Steel fiber reinforced polymer (SRP) composite materials, which consist of continuous unidirectional steel wires (cords) embedded in a polymeric matrix, have recently emerged as an effective solution for strengthening of reinforced concrete (RC) structures. SRP is bonded to the surface of RC structures by the same matrix to provide external reinforcement. Interfacial debonding between the SRP and concrete is a primary concern in this type of application. This study aimed to investigate the bond characteristics between SRP and concrete determined by single-lap direct shear tests with different composite bonded lengths and fiber sheet densities (cord spacings). Specimens with medium density fibers failed mainly due to composite debonding, whereas those with low density fibers failed due to fiber rupture. Results of specimens that exhibited debonding were used to determine the bond-slip relationship of the SRP-concrete interface and to predict the full-range load response, which was in good agreement with the experimental results. A database of SRP-concrete direct shear tests reported in the literature was also established. Four analytical equations derived for fiber reinforced polymer (FRP)-concrete debonding were evaluated based on the database results and were found to predict the maximum load within approximately 15% error on average, however, they all underestimated the effective bond length. [ABSTRACT FROM AUTHOR]

An accurate bond-slip model is of fundamental importance to analyze the response of fiber-reinforced cementitious matrix (FRCM) composite-strengthened structures. This study proposes a method to determine the bond-slip model of FRCM-concrete joints based on longitudinal fiber strains. First, discrete strain profiles measured with strain gauges were fitted by a continuous function ε(y) , where y is the coordinate along the bonded length. Then the slip s(y) and shear stress τ (y) along the composite bonded length were obtained by integration and derivation of ε(y) , respectively. The debonding load and peak load from single-lap direct shear specimens were predicted by the fitted function ε(y) and showed good agreement with test results. From the plot of the τ(s) relationship obtained from ε(y) , an alternative, closed-form, continuous bond-slip relationship was obtained based on the maximum shear stress τm and the corresponding slip sm. The fracture energy was compared for both relationships and was in reasonable agreement with values reported in previous studies. [ABSTRACT FROM AUTHOR]