ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING)
Year:2012 | Volume:13 | Issue:4|Papers Count:10

In the first part of the present paper, a numerical method called spectral finite element method (SFEM) is presented. As shown there, SFEM offered a promising performance in simulating wave scattering phenomena in plates, with less computational effort while obtaining the highest resolution. The forward solution of wave scattering phenomenon based on the differential waveform of highest resolution plays a crucial role for detection of through-thickness crack in plates, as an inverse problem. Therefore, the results of the first part of the paper have been used in the second present part, in which a novel approach in wave scattering based crack detection, according to the concept of Time Delay (Differences) Of Arrival (TDOA) has been presented. In the past decades, TDOA and its related concepts have been applied generally on the problem of localization and pursuing sound sources in robotics, electronics engineering, control engineering, and so on. However, in this study TDOA is employed for crack detection problems for the first time. Introducing TDOA has provided a robust algorithm for crack detection which is highly sensitive to the crack location and size. Using the proposed algorithm, a couple of numerical case studies has been studied, in which the predicted crack location and dimensions are quite encouraging.

The present work aims to study the seismic performance of exterior shear wall-slab joint with non-conventional reinforcement detailing. Four joint sub assemblages were tested under reverse cyclic loading applied at the end of the slab. The specimens were sorted into two types based on the joint reinforcement detailing. Type 1 model comprises of two joint assemblages having joint detailing as per the conventional detailing of slab bars at the joint.The second set of models (Type 2) comprises of two specimens having additional cross bracing reinforcements for the joints detailed as per the provisions given for beam–column joint in IS 13920: 1993. Analytical investigations were employed to compare the experimental results. The experimental results and analytical studies indicate that additional cross bracing reinforcements improves the seismic performance.

In this paper, optimal design of barrel vaults is performed using the Improved Big Bang-Big Crunch (IBB-BC) method. This method can be used for problems with continuous and discrete variables. Here, double layer braced barrel vaults are optimized considering weight of the structure as the objective function, where the necessary constraints are satisfied. The cross sectional areas are considered as continuous variables.The algorithm is based on the Big Bang-Big Crunch (BB-BC) and Harmony Search (HS). The BB-BC applies for global optimization and the HS deals with variable constraints. After a number of sequential Big Bangs and Big Crunches, where the distribution of randomness within the search space during the Big Bang becomes smaller and smaller about the average point computed during the Big Crunch, the algorithm converges to a solution. In the proposed method, similar to HPSO, HS is used for controlling the variable constraints.

Jacketing a reinforced concrete column by Fibre Reinforced Polymer (FRP) wraps primarily improves column performance, not because the jacket itself carries some fraction of the axial load applied to the column, but rather because, it provides lateral confining pressure to the column. This confining pressure places the concrete in a triaxial state of stress, altering the load-deformation characteristics of concrete. But contribution of wraps in improving the load carrying capacity of columns still remains controversial and there is need to develop suitable confining models for FRP wraps. Simple analytical equations based on confinement model developed by Richart et al. with modified value of confinement effectiveness coefficient were proposed to predict the axial load carrying capacity of FRP confined circular columns under axial loading. The proposed equations were validated through the previous experimental database available in literature. A good correlation is obtained between the proposed equations and the existing experimental results. The confined concrete strength from tests was compared with the results from the developed empirical equations and the comparisons are favorable.

FEMA440 proposed coefficient method considers the effect of stiffness degradation and strength deterioration by C2 modification factor. This factor is obtained by SDOF oscillator responses with few degrading hysteresis behaviors. This paper studies the ability of coefficient method to estimate displacement demands of MDOF buildings with mild and severe degradations. Performance of Intermediate and Special steel moment frames is compared separately by utilization of nonlinear static and dynamic analyses. Error values show a good correlation between nonlinear static and dynamic responses.

In order to address environmental effects associated with Portland cement, there is need to develop alternative binders to make concrete. An effort in this regard is the development of geopolymer concrete, synthesized from the materials of geological origin or by product materials such as fly ash, which are rich in silicon and aluminum. This paper presents results of an experimental program on the mechanical properties such as density, compressive strength, split tensile strength and flexural strength of Geopolymer Concrete Composites (GPCC) containing 90% Fly ash (FA), 10% Ordinary Portland Cement (OPC), alkaline liquids and glass fibers. The effect of inclusion of glass fibers on the density, Compressive Strength, Split Tensile strength and Flexural strength of hardened GPCC was studied. Alkaline liquid to fly ash ratio was fixed as 0.4 with 10% of fly ash replaced by OPC in mass basis. Glass fibers were added to the mix in volume fractions of 0.01%, 0.02% and 0.03% by volume of concrete.The influence of fiber content in terms of volume fraction on the compressive strength, split tensile strength and flexural strengths of GPCC is presented. Based on the test results, empirical expressions were developed to predict split tensile strength and flexural strength of glass fiber reinforced GPCC in terms of its compressive strength.

Self-consolidating concrete (SCC) has been used increasingly over the last two decades, especially in the pre-cast concrete industry because of its ability to consolidate without vibration even in congested areas. The development of SCC mixture design has been driven mostly by private companies who desired to utilize SCC's advantages and consequently there exists limited public information regarding the performance of SCC mixtures.The present study has attempted to present an experimental study on fresh and hardened properties of SCCs containing Volcanic Pumice (VP) as natural pozzolans which was used for both cement and filler replacements, in comparison with ordinary SCC mixture, SCCs containing Silica Fume (SF) and conventionally vibrated concrete mixture. Properties such as slump-flow, J-ring, L-box, V-funnel and sieve segregation resistance were investigated for fresh concrete and tests such as compressive strength, water and chloride-ion permeability and capillary water absorption at various days were performed for hardened concrete. The results indicate that natural pozzolanic materials such as VP can be used to produce SCCs. In addition, the results prove that natural pozzolans have enhanced the mechanical properties and durability of SCC and reduced the chloride penetration, significantly.

Iran is a country of particular geopolitical significance owing to its location in the Middle East and central Eurasia. Owing to its strategic location, Iran has been the centre of attention for traders, businessmen and big powers for a long time.Therefore, it might be exposed at risk. The recognition necessity of risk and the resisting trend is essential for structural engineering. The analysis and design of reinforced concrete structures subjected to extreme loading condition such as blast loads require a detailed understanding of blast phenomena and the dynamic response of various structural elements. In this paper, the response of RC columns subjected to constant axial loads and lateral blast loads is examined. Different shapes of columns, i.e. square, rectangular and circular shape, are considered in this research. A nonlinear finite element program is used to model RC columns with different boundary conditions and using the mesh less method to reduce mesh distortions. For the response calculations, a constant axial force is first applied to the column and then, lateral blast load is applied and the response time history is calculated. Blast load effects on the columns quantified in terms of failure mechanisms through simulation of the whole column detailing in the nonlinear finite element program.According to the analysis results, a retrofitting scheme using FRP wraps is designed and validated with a blast load test. Comparison of results clearly demonstrates that columns with externally FRP retrofitting can withstand higher levels of blast loads. It means that retrofitting RC columns with FRP is a proficient way to ensure protection of buildings under the blast loading.

This paper presents the results of experimental, analytical and numerical studies concerning the flexural strengthening of RC beams using externally bonded High Performance Fibre Reinforced Cementitious Composites (HPFRCCs) like Slurry Infiltrated Fibre CONcrete (SIFCON) and Slurry Infiltrated Mat CONcrete (SIMCON). A total of ten reinforced concrete beams were cast and tested in the laboratory over an effective span of 3000 mm.Eight beams were strengthened with bonded SIFCON and SIMCON laminates at the bottom under virgin condition and tested until failure; the remaining two beams were used as control specimen. Static responses of all the beams were evaluated in terms of strength, stiffness, ductility ratio, energy absorption capacity factor, compositeness between laminate and concrete, and the associated failure modes. Comparisons were made between experimental, analytical and numerical results of SIFCON and SIMCON. The results show that the strengthened beams exhibit increased flexural strength, enhanced flexural stiffness, and composite action until failure.

This paper presents the seismic behavior of exterior beam-column joints with square spiral confinement in the joint region along with different reinforcement detailing for anchorage of beam bars, confinement in joint and additional reinforcement in beam and column. The performance of the specimens are compared in terms of lateral load-displacement hysteresis loop, load ratio, percent of initial stiffness versus displacement curves, total energy dissipation, beam rotation at distances of D and 2D, strain in beam main bars and crack pattern. Among all, the specimen with inclined bars from beam to column (named as SS2) was the most effective considering all the parameters taken for comparison. It is concluded that inclined bars from column to beam in SS2 can successfully move the plastic hinge away from the column face.