Journal of Engineering and Technological Sciences
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Collapse Risks of Fail-Safe RC Frames Due to Earthquakes: Fragility Assessments
Get PDFThe objective of this study was to determine the collapse risk of fail-safe reinforced concrete (RC) frames due to earthquakes by newly developed fragility curves. The curves were constructed based on the collapse mechanism, instead of measures of lateral drift as customarily adopted. The procedure was applied to RC open frames that were seismic resistant. A fail-safe mechanism was imposed by allowing plastic hinges to be formed mainly in the beams. This automatically satisfied the stronger column-weaker beam requirement; shear failure was neither tolerated anywhere in the columns nor in the beams. Two kinds of fail-safe RC frames were investigated: special moment resisting frames (SMF) and ordinary moment resisting frames (OMF). Their earthquake collapse risk was computed and compared. Inelastic time history (NLTH) and the non-linear static procedure (NSP) were conducted to assess their structural performance. The results showed among others that the fail-safe OMF had lower collapse risk than the fail-safe SMF. The collapse prevention performance level in NLTH could only be achieved for the fail-safe frames. The non-linear time history analysis should be the only method used for seismic reevaluation/safety checking of building frame structures
Developing Sub-wavelength Sound Absorber Based on Coiled Up Tube Resonator
Get PDFSub-wavelength sound absorbers are attractive for dealing with noise control at low-frequency (long-wavelength) sounds. To be efficient in absorbing the sound energy, resonator based absorbers are preferable over fibrous porous ones. In this paper, a coiling up space approach is introduced to a tube resonator system in order to realize a sub-wavelength absorber structure. In this way, the air channel of the tube resonator is a coplanar coiled up channel rather than a straight channel as found in conventional tube resonators. The effect of the geometrical properties of the aperture and the air channel were studied further to look at their relationship to impedance mismatch, which coiling up systems typically suffer from. It was found that the proposed approach could realize a sub-wavelength absorber system up to 1/32 wavelength of peak sound absorption. Selection of the shape and dimensions of the aperture must be done with great care as indicated by the measurement results. Moreover, the behavior of the coiled up tube resonator deviates from that of the straight tube as the reflection factor is increased, although the target resonance frequency is close to the target. It was also found that a squared aperture shape as well as increasing the cavity thickness is useful to deal with impedance mismatch
Development of Nationwide Surface Spectral Acceleration Maps for Earthquake Resistant Design of Bridges Based on National Hazard Maps of Indonesia 2017
Get PDFSpectral acceleration at the ground surface, including peak ground acceleration, provides essential information for earthquake resistant design and must be provided to bridge engineers in easily accessible media. Spectra acceleration maps are one way to deliver such information, but unfortunately the most recent Indonesian earthquake resistant design standard for bridges, SNI 2833-2016, only provides maps of earthquake hazard at bedrock. The development of earthquake acceleration maps at the ground surface for Indonesia in this study was based on earthquake hazard maps at bedrock with probability of exceedance (PE) 7% in 75 years, i.e. equal to an earthquake with a return period of 1034 years. Site conditions were adopted from the nationwide Vs30 map of Indonesia proposed by Irsyam (2017), which is a modified version of the Vs30 map proposed by Imamura & Furuta (2015). Site conditions combined with hazard value were used to determine the amplification factors according to the criteria in SNI 2833-2016 and then multiplied with hazard at bedrock to obtain surface spectra acceleration maps. The resulting maps are very useful for determining earthquake loads for bridge design at the preliminary design stage. Improvements to incorporate more advanced calculation methods and updated data in a future research are recommended and very feasible
An Evaluation of Pile-Raft Interaction in Cohesive Soils using 3D Finite Element Method
Get PDFThis paper presents the results of a numerical study of soil-structure interaction in a piled-raft foundation system in clay soil by reviewing the deformation and load transfer mechanism of the piled-raft foundation system. ABAQUS was used to evaluate the interaction in the system, while a Mohr-Coulomb constitutive model was chosen to model the clay soil. Verification of the model was conducted by comparing the simulation result to an experimental laboratory result. The verification result showed that the model used in this research agreed well with the experimental laboratory research. Subsequently, a parametric study was performed by varying the pile spacing, raft size, pile length, and raft thickness. A parametric study was conducted on very stiff and hard clays. This study concludes that the load transfer mechanism in a piled-raft foundation system between the pile and raft foundation occurs after the pile reaches its ultimate capacity and is in the plastic zone
Comparative Study of Building Envelope Cooling Loads in Al-Amarah City, Iraq
Get PDFIn recent years, the summer season in Iraq has become longer and hotter than before, leading to high cooling loads inside buildings and increased demand for electrical energy. The use of sustainable energy and insulation techniques for building envelopes are reasonable solutions for overcoming harsh weather conditions and reaching acceptable thermal comfort levels. In this study, a survey on more than 60 residential buildings in Al-Amarah City, Iraq, was conducted on 21 July 2018 to examine the nature of the most common construction materials used in the building envelopes. Furthermore, the cooling loads of building envelope elements, e.g. roof, external walls and windows, was calculated using the cooling load temperature difference/solar cooling load/cooling load factor method of ASHRAE. The results were tabulated and compared for each combination of elements. The results showed that reflective glass is the optimal choice for exterior windows. The 'clay"“insulation"“fired clay bricks"“cement mortar' and 'cement mortar"“thermo-stone bricks"“cement mortar"“gypsum mortar' combination layers performed well for roof and external wall installations, respectively. Several recommendations were deduced from this study, which can be used as guidelines for construction authorities in Al-Amarah City and individuals interested in energy-efficient buildings
Modeling and Designing of a Novel Lab-scale Passive Solar Still
Get PDFThe solar still is an emerging water distillation technology gaining popularity among the scientific community. Achieving a high throughput and/or performance in solar stills remains an unresolved challenge. In this study, the feasibility of utilizing solar distillation systems for large water production was investigated. A solar still was designed and tested with different brackish waters under solar insolation in Los Angeles from March to April. The inner surface area of the cell was about 12.7 cm 12.7 cm with a maximum volume of 322.6 cm3. The still performance was evaluated experimentally and modeled theoretically, showing a good agreement between theory and experiment. The maximum achieved efficiency was 20.54%, corresponding to a freshwater production of 384.4 mL/day·m2 (6.2 mL/day). Lowering the feed amounts from 120 to 30 mL/day resulted in increasing the experimental performance from 6% to 18.3% due to the quick ramp in heat of vaporization; however, the production rates decreased from 446.4 to 341 mL/day·m2 (7.2 to 5.5 mL/day). Polystyrene insulation and a blackened walls/basin can improve the performance by maintaining high temperature, decreasing heat loss, and enhancing solar absorption. It is concluded that still materials, insolation rate, and inclination angle are the most critical design factors
Study on the Mechanism of Particle Breakage under New Composite Loads
Get PDFA theoretical model of particle breakage under a novel combination of dynamic and static loads is presented in this paper. In order to enhance the capability of the actual physical and mechanical properties towards rocks, parallel connector parameters of a bonded particle model (BPM) from the discrete element method (DEM) were investigated by uniaxial compression tests. Then, the efficiency evaluation index system of particle breakage was defined and different simulations of various parameters were set, i.e. the speed of the moving plate, the curvature of the moving plate, the curvature of the fixed plate, the space between the two plates, and the initial particle radius. The mechanism of particle breakage was analyzed by the relationships between the efficiency evaluation index and various parameters. The investigation of particle breakage theory and law can help to design and improve crushing equipment, reduce the energy consumption of the crusher, and improve the quality of the broken product