Seismic Shear Strengthening of Reinforced Concrete Short Columns Using Ferrocement with Expanded Metal

Typical reinforced concrete short column is brittle in shear rather than flexure under lateral cyclic loading due to its shear deficiency.  This paper presents the improvement of seismic behaviour of the reinforced concrete short columns which were strengthened by using ferrocement with expanded metal.  Full scale experiments were conducted for two strengthened concrete columns with different volume fractions of expanded metal and the control specimen under lateral cyclic loading.  It was found that the seismic behaviour in terms of the shear strength, stiffness, displacement ductility, and energy dissipation were significantly improved.  The expanded metal mesh with the high specific surface provided the better performance for controlling the crack propagation.  The brittle shear failure mode of the stirrup was reduced and the ductile flexure mode of the longitudinal reinforcement was dominant.  The reduced shear force of the stirrup was compensated by the shear force of the expanded metal reinforcement which experienced relatively large strain.  The technique of steel angle installation at the corners of column can successfully prevent the effect of sharpened corner wrapping of the mesh.  A model to predict the shear strength of the strengthened column is presented in term of the global efficiency factor for expanded mental.    &nbsp

Experimental and Analytical Study on Reinforcing Steels with Threaded Mechanical Couplers under Monotonic and Cyclic Loadings

This study performs the experimental and analytical investigation on the effect of mechanical couplers on the axial behavior of spliced reinforcing bars. The effect of unsupported-length-to-bar-diameter (L/D) ratios on the monotonic and cyclic behavior was observed. The test configurations in monotonic tension, compression, and cyclic tests included reinforcing bars with and without threaded mechanical couplers. Specimens with mechanical couplers have higher strength in compression than the bars without couplers, especially when L/D is less than 10. The procedure for determining the effective unsupported length for bars with a mechanical splice was proposed. And the observation on the energy dissipation confirmed the proposed method.  The calculated hysteretic loops using the modified unsupported length model of the bar with mechanical splice agreed well with the test result

Seismic Strengthening of RC Frame and Brick Infill Panel using Ferrocement and Expanded Metal

This paper presents the strengthening of reinforced concrete frame and brick infill panel by using ferrocement technique reinforced with expanded metal. Analytical models of the strengthened frame and infill panel were proposed. An experimental study on the strengthened frames was conducted to verify the proposed models. Two control specimens and two strengthened specimens were compared: the bare frame and the infilled frame. Special strengthening techniques were employed to protect against two major failures: the beam and columns of the frame were fully strengthened to prevent shear failure, and the infill panel was protected against corner compression failure. The frames were investigated under constant vertical load and lateral cyclic load. The seismic behavior of the retrofit frames was compared with the control specimens. The strengthened frames showed the significant increase of strength up to 64% and 87%, and the ductility capacity was also improved 77% and 66% for the bare frame and the infilled frame, respectively. The proposed model of strengthening for the frame and infill panel predicted the lateral resistance of the RC infilled frame with a reasonable accuracy when compared to the observed experimental results

Optimal Multi-Reservoir Operation for Hydropower Production in the Nam Ngum River Basin

This research aims to investigate optimal hydropower production of multi-reservoirs in Lao PDR and develop optimal reservoir rule curves. The Nam Ngum 1 and 2 (NN1 and NN2, respectively) reservoirs in the Nam Ngum River basin (NNRB), which is located in the middle of Laos, are selected as study areas. Mixed integer nonlinear programming (MINLP) is developed as an optimization model to maximize the hydropower production of joint reservoir operation of NN1 and NN2. The optimal operation rule curves are established by using the storage level estimated by the optimization model. Given the limited sideflow data, an integrated flood analysis system (IFAS) and water balance equation are used to simulate the sideflow into NN1 reservoir. A good fit is observed between the monthly streamflow simulated by IFAS and that calculated by the water balance equation. Compared with the observed data, the MINLP model can increase the annual and monthly hydropower production by 20.22% (6.01% and 14.21% for NN1 and NN2, respectively). The water storage level estimated by the MINLP model is used to build the operation rule curves. Results show that the MINLP model of multi-reservoir is a useful and effective approach for multi-reservoir operations and is expected to hold high application value for similar reservoirs in NNRB

Cross-Sectoral Analysis of Water Usage in Thailand Using Input–Output Model

Thailand currently ranks third among the most water-intensive countries in the world. The percentage shares of water demand in the country’s agriculture, manufacturing, and service sectors, which are major economic sectors, are 75%, 3%, and 5%, respectively. With the continuous growth of the economy, the demand for water is steadily rising, while the expansion of water supply remains constrained by several factors and the water supply is also affected by climate change. This study uses the input–output model to examine the relationship between water usage and the economic system in Thailand in 2010. The constructed input–output model is the integration of the Leontief inverse matrix, the matrix of water usage, and the details of the gross domestic product (GDP). The model indicates the linkage between GDP expansion and water demand in both direct and indirect usage. The computation result obtained from the model indicates that the agricultural sector is the major water user, with its ratio of direct water use being the highest. The manufacturing sector records the highest ratio of indirect water use, which is influenced by its supply chain comprising the agriculture and service sectors. This model and its results may serve as the main foundation for the design of economic and environmental policies oriented toward optimizing water demand and supply. The model can also be extended and enriched with detailed mechanisms of economic behavior to allow further complex analyses such as water pricing policies

Strengthening of Shear-Critical RC Columns by High-Strength Steel-Rod Collars

This research investigates the strengthening of shear-dominated reinforced concrete (RC) square columns using the high-strength steel-rod collars, which enhance confinement by steel rods around the column perimeter. This method is less intrusive to the existing building with infilled walls because steel rods can penetrate through the walls with minimal openings (holes) at the location of collars. In this study, one control specimen and two specimens strengthened by steel-rod collars were tested. All specimens were subjected to lateral cyclic loading along with a constant axial load. The difference between the two strengthened specimens were the spacing of steel-rod collars mounted on the columns. The spacing of steel-rod collars was 200 mm in the column specimen SC-200, while the other strengthened specimen, SC-100 has a spacing of 100 mm. The unstrengthened column failed in shear while the strengthened columns failed in flexure. In addition, the strengthened specimens failed at the higher load and ductility. Comparing to the unstrengthened column, the lateral load capacity and ductility ratio of the column SC-200 increase by 18 % and 59%, respectively. While, the lateral load and ductility ratio of SC-100 increase by 16% and 69%, respectively. Furthermore, the finite element models of all column specimens are developed using the OpenSees program. The analysis results are found in a close agreement with the experimental results

Deterministic Seismic Hazard Analysis in Thailand using Active Fault Data

To develop seismic design criteria for buildings, seismic hazard analysis is required to estimate the ground motion intensity with criteria such as peak ground acceleration (PGA). The seismic hazard can be analyzed by using two approaches: deterministic seismic hazard analysis (DSHA) and probabilistic seismic hazard analysis (PSHA). In these two approaches, the seismic hazard is evaluated from past earthquake events and active faults data. In Thailand, seismic hazard is classified in the low lying regions; however, in recently years, earthquakes have occurred frequently in the North of Thailand. To prevent and reduce damage due to earthquakes in the future, determination of seismic hazard is needed. This research proposes a deterministic seismic hazard map evaluated from nineteen active faults affecting Thailand. Two types of active faults are considered: first, an active fault in a subduction zone and second, a crustal fault. The seismic hazard is evaluated by using a ground motion prediction equation (GMPEs). Four GMPEs are weighted equally for seismic crustal fault, and two GMPEs are weighted equally for a seismic subduction zone. The hypocentral distance is used to evaluate the seismic hazard for all ground motion prediction equations. The Northern part and the Western part of Thailand are high seismic hazard regions, because there are active faults with the large possibility of earthquakes of a maximum magnitude. The seismic hazards in the North, West and Northeast of Thailand are about 0.60 g. The seismic hazard in Bangkok is about 0.25 g due to the Three Pagoda fault and Sri Sawat fault. The seismic hazard in the South of Thailand is about 0.40 g

Dimensional analysis of the earthquake-induced pounding between adjacent structures

In this paper the dynamic response of two and three pounding oscillators subjected to pulse-type excitations is revisited with dimensional analysis. Using Buckingham's Π-theorem the number of variables that govern the response of the system is reduced by three. When the response is presented in the dimensionless Π-terms remarkable order emerges. It is shown that regardless of the acceleration level and duration of the pulse all response spectra become self-similar and follow a single master curve. This is true despite the realization of finite duration contacts with increasing durations as the excitation level increases. All physically realizable contacts (impacts, continuous contacts, and detachments) are captured via a linear complementarity approach. The study confirms the existence of three spectral regions. The response of the most flexible among the two oscillators amplifies in the low range of the frequency spectrum (flexible structures); whereas, the response of the most stiff among the two oscillators amplifies at the upper range of the frequency spectrum (stiff structures). Most importantly, the study shows that pounding structures such as colliding buildings or interacting bridge segments may be most vulnerable for excitations with frequencies very different from their natural eigenfrequencies. Finally, by applying the concept of intermediate asymptotics, the study unveils that the dimensionless response of two pounding oscillators follows a scaling law with respect to the mass ratio, or in mathematical terms, that the response exhibits an incomplete self-similarity or self-similarity of the second kind with respect to the mass ratio

Effective linear damping and stiffness coefficients of nonlinear systems for design spectrum based analysis

A stochastic approach for obtaining reliable estimates of the peak response of nonlinear systems to excitations specified via a design seismic spectrum is proposed. This is achieved in an efficient manner without resorting to numerical integration of the governing nonlinear equations of motion. First, a numerical scheme is utilized to derive a power spectrum which is compatible in a stochastic sense with a given design spectrum. This power spectrum is then treated as the excitation spectrum to determine effective damping and stiffness coefficients corresponding to an equivalent linear system (ELS) via a statistical linearization scheme. Further, the obtained coefficients are used in conjunction with the (linear) design spectrum to estimate the peak response of the original nonlinear systems. The cases of systems with piecewise linear stiffness nonlinearity, along with bilinear hysteretic systems are considered. The seismic severity is specified by the elastic design spectrum prescribed by the European aseismic code provisions (EC8). Monte Carlo simulations pertaining to an ensemble of nonstationary EC8 design spectrum compatible accelerograms are conducted to confirm that the average peak response of the nonlinear systems compare reasonably well with that of the ELS, within the known level of accuracy furnished by the statistical linearization method. In this manner, the proposed approach yields ELS which can replace the original nonlinear systems in carrying out computationally efficient analyses in the initial stages of the aseismic design of structures under severe seismic excitations specified in terms of a design spectrum