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An external ENTA damper system or steel frame seismic retrofit approach was investigated for historic reinforced concrete (RC) buildings. RC frame specimens were evaluated under cyclic lateral loading to confirm the external retrofit approach. The investigation involved an examination and comparison of hysteresis-based behaviors, such as strength, ductility, and energy dissipation, with the aim of gaining a deeper comprehension of the distinct impacts of external retrofit systems on seismic performance. The experimental findings indicate that the implementation of the external ENTA damper system and steel frame effectively enhanced the stiffness and durability of vulnerable RC moment frames, while maintaining their deformation capacity. The enhancement of the energy-dissipation capacity was achieved by the use of measures to prevent premature failure of the RC beam-column joints. On the basis of the experimental results, the failure mechanism of the RC frame was discussed, considering the shear connection behavior. In order to further validate the experimental results, analytical modeling of the undamaged specimens was carried out using the LS-DYNA program. The test strengths of the frame specimens were evaluated and compared to the anticipated values derived from a simple plastic mechanism. • The ENTA damper systems increased the load-bearing capacity of the RC frame structures. • ENTA damper systems significantly improved the stiffness resistance and energy absorption of RC frame structures. • The ENTA damper systems prevented serious damage to the beam-column joints in RC frame structures. • The FE model appropriately predicted shear, ductile and behavior concrete failure in RC frame and retrofitted RC frame. [ABSTRACT FROM AUTHOR]

Blast loading and seismic excitations are widely recognized as the most detrimental occurrences that a building structure may encounter throughout its lifespan. Therefore, this study investigated the retrofitting capacity of external devices (ENTA damper systems) for reinforced concrete (RC) frames in term of enhancing their resistance under the combined effects of blast and seismic loads. This study presents the establishment of finite element (FE) models for retrofitted RC frames with ENTA damper systems through the utilization of the dynamic analysis software LS-DYNA. The investigation involved the validation for blast performance of RC column in order to identify the most effective method for modeling blasts. Additionally, the study aimed to validate the performance of RC frame models through effects of ENTA damper systems under seismic loading. Subsequently, a performance evaluation of RC frame structures was carried out to examine the impact of the ENTA damper systems when subjected to blast loading. The findings of the study indicate that the use of external ENTA damper systems effectively enhanced the rigidity and structural integrity of RC frames, while maintaining their ability to resist deformation. Finally, the damage assessment of blast and seismic performance is investigated based on various parameters such as ductility, drift and energy-based damage limits. • Finding the suitable model blasts based on the blast performance of RC column. • Validating performance of the RC frame models under seismic loading. • Investigating the blast performance of RC frame and retrofitted RC frame. • Considering the damage performance of RC frames under blast and seismic loadings. [ABSTRACT FROM AUTHOR]

Introduction: The aim of this research was to verify that ultraviolet light (UV)-photofunctionalization improves the success rate and biomechanical stability of miniscrews regardless of length, and to evaluate the comparability of biomechanical stability between UV-photofunctionalized miniscrews with short lengths and untreated miniscrews with conventional lengths.Methods: Eight male beagles (age, 12-15 months; weight, 10-13 kg) received a total of 64 miniscrews, including 7-mm and 4-mm untreated and UV-photofunctionalized, acid-etched miniscrews with the use of a random block design. The cumulative success rates were examined in all studied groups. The insertion and removal torques and screw mobility were measured. Microcomputed tomographic scans and histomorphometric analyses were performed at 8 weeks postoperatively.Results: The success rates of 7-mm UV-untreated and UV-photofunctionalized miniscrews were 87.5% and 100%, respectively, vs 43.8% for the 4-mm UV-untreated and 4-mm UV-photofunctionalized miniscrews. The rates were significantly different in accordance with the length (P <0.001). There were no differences in the insertion and removal torque and screw mobility between groups according to the length or UV treatment. However, the 4-mm UV-untreated miniscrews yielded a mean bone area ratio of 6.35 ± 7.43%, whereas the 7-mm UV-photofunctionalized miniscrew yielded a mean ratio of 32.17 ± 8.34% (P = 0.037).Conclusions: The UV-photofunctionalization significantly increased the biomechanical stability and led to increased bone and miniscrew contact area in dogs with miniscrews of the same length. However, the most important factor that affected the success rate of the miniscrew was the length. [ABSTRACT FROM AUTHOR]

Fiber reinforced polymer (FRP) materials continue to demonstrate outstanding performance for strengthening and repairing reinforced concrete structures. However, one of the most significant problems that still has to be tackled is premature failure brought on by the FRP debonding. This research sought to determine how damaged RC columns could be strengthened with aramid (one type of FRP) composites and how that would affect their seismic responses. To further understand the individual effects of each strengthening material on seismic performance, hysteretic responses, such as strength, ductility, and energy dissipation, were examined and compared. Analytical modeling is validated based on the experimental results. Experimental results are validated with comparative study against other solid experimental results within the broader field. Effective bond length (EBL) is crucial for understanding the bonding between aramid fibers and concrete, however various models have different ways of calculating the value of EBL. Therefore, this research examined earlier experimental investigations of EBL and employing finite element (FE) methods established a novel relationship between the EBL and the aramid-to-concrete bond, based on experimental results. • Experimental assessment with various specimens such as RC columns and RC columns with retrofitted aramid sheets. • Developing the FE model to investigate the response of the structural columns. • Considering the effect of the retrofit system on the RC columns. • Proposing the best-fit empirical model between the effective bond length (EBL) and the aramid-to-concrete bond. [ABSTRACT FROM AUTHOR]

Column jacketing techniques have been widely used to improve the seismic performance of existing reinforced concrete buildings and to mitigate additional damage induced by subsequent earthquakes to earthquake-damaged structures. To numerically assess damage mitigation of structures due to column jacketing under successive earthquakes, this study proposes a numerical modeling technique for shear-critical reinforced concrete columns retrofitted and repaired using fiber-reinforced polymer wraps and validates the simulated results with existing experimental data. A non-ductile reinforced concrete frame with the potential of column shear failure is then selected and modeled using the proposed modeling technique to evaluate the effect of FRP retrofit and repair upon mainshock and aftershock responses. In addition, two rehabilitation parameters such as story-related rehabilitation and number of FRP wraps are selected, and used to create rehabilitated frame models to maximize the effectiveness of FRP installations for the as-built frame under successive earthquakes. This effectiveness is examined in terms of the damage level of maximum and residual deformation. [ABSTRACT FROM AUTHOR]

Many existing reinforced concrete buildings designed in accordance with pre-1971 codes are generally dominated by weak column-strong beam behavior under seismic loading due to inadequate reinforcement detailing. This behavior can lead to premature failure under seismic loads from damage concentrated in the first story of the structure. This paper presents the results of an experimental investigation into the seismic response of a full-scale, two-story non-ductile reinforced concrete frame. The frame was retrofitted with a fiber-reinforced polymer jacketing system on the first story columns to mitigate seismic vulnerability. Shake weight testing was performed to investigate the dynamic performance of the retrofitted building structure in terms of the modal response, inter-story drift, and effectiveness of the fiber-reinforced polymer jacketing system. The results demonstrate that the retrofit scheme helped develop a more uniform story drift distribution, working to counter the soft-story mechanism commonly found in reinforced concrete frames designed during this period. [ABSTRACT FROM AUTHOR]

Although provisions available in current design codes that take account of the presence of anchor plates, the existing provisions take no account of the effects of anchor plate size. In this study, the effect of anchor plate size on the concrete breakout strength in tension was evaluated for a single anchor system used in a thin-walled concrete wall panel. Twenty-seven specimens were tested to investigate the effects of anchor plate width and thickness. The test results show that concrete breakout strength is considerably improved with increased anchor plate size, with the rate of improvement diminishing in very large anchor plates. A simplified analytical model was proposed to determine the optimal width and thickness of anchor plates. The predicted optimal values were validated with the test results; the proposed analytical model is capable of determining the proper size of anchor plates in thin-walled concrete panels. [ABSTRACT FROM AUTHOR]

In building design codes, buildings having less than 3 stories and a floor area less than 1000 m 2 are generally defined as small-scale buildings, and these are generally exempted from seismic requirements. To prevent potential loss of life and economic damage in the event of an earthquake, such buildings should be retrofitted so as to conform to current seismic design codes. In this study, a seismic retrofit scheme using buckling-restrained knee brace (BRKBs) was developed for a 2-story non-seismic gravity-designed steel frame building using the fragility contour method. To develop an effective retrofit scheme using BRKB for this building, 75 types of BRKB analytical models were used to achieve the desired performance levels and analyzed. Then, the seismic performance of the building before and after the retrofit was evaluated using the fragility contour method, and the improvement in the performance level of the probability against the structural limit state, such as component failures and structural collapse, was investigated. Based on the analytical studies, the most effective BRKB model for the retrofit scheme was proposed based on various scenarios in terms of the weight of the developed BRKB models. This study shows that the fragility contour method can be used for rapid evaluations and should be an effective tool for structural engineers to perform the seismic retrofit of buildings. [ABSTRACT FROM AUTHOR]

• Effect of FRP jacketing system on seismic damage mitigation of non-ductile RC frames. • Investigation of seismic performance against various seismic loading hazard levels. • Identification of critical retrofit parameters influencing on the seismic performance. • Establishment of retrofit schemes for confinement and stiffness-related parameters. Many existing reinforced concrete building structures designed for gravity loads have seismic vulnerabilities owing to their deficiency in column detailing. A column jacketing system with prefabricated fiber-reinforced polymer materials provides additional confinement and stiffness to existing columns and mitigates their seismic vulnerabilities. This paper presents a seismic retrofit strategy for a low-rise gravity-designed reinforced concrete building frame for maximizing the retrofit effect against low, moderate, and high seismic hazard levels. The retrofit parametric models were created by varying the confinement and stiffness-related parameters and then simulated under various seismic loading scenarios. To establish the seismic strengthening strategy, the effectiveness of the retrofit system was examined in terms of its confinement and stiffness-related parameters. This retrofit effect was computed by comparing energy-based seismic demands between retrofitted and non-retrofitted models. Based on the parametric analysis, the critical parameters of the retrofit system were determined depending on the seismic hazard levels. Thus, the certain threshold values of the retrofit parameters for the seismic hazard levels to maximize the effectiveness of the retrofit system were proposed as the retrofit design scheme. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the seismic behavior of double-layer barrel vault systems with different open angles through analytical and experimental studies with modeling of thin-walled steel tubes. For the analytical study, different six open angles and four fundamental frequencies were incorporated into the barrel vault analysis models and analyzed. A total of 24 double-layer structures were developed using the MIDAS computer analysis program and these structures were subjected to three different ground motions with a 5% damping ratio. The characteristics of the dynamic responses for the X, Y, and Z directions of the analytical model, subjected to both horizontal and vertical earthquakes, were investigated. In addition to the analytical study, an experimental study using scaled down thin-walled steel tube models was undertaken using a shaking table test. Comparing the analytical and experimental studies, the dynamic behaviors were very similar in terms of the distributions of the acceleration responses. Both the analytical and experimental models had maximum values at the 1/4 and 3/4 nodes, while having relatively smaller responses at the center node from horizontal earthquakes. It is believed that the barrel vault model with an open angle of 90 degrees has the most advantageous shape of the analytical barrel vault models used in this study. [Copyright &y& Elsevier]

Piloti-type reinforced concrete building structures have vertically irregular configurations composing a moment frame for parking spaces in the lower story and heavy-weight shear wall system for residential spaces in the upper stories. Due to these vertically irregular configurations, such building structures are governed by a soft-story mechanism, damage concentration on the first story. Since the 2017 Pohang earthquake led to severe damage to the piloti-type building structures on a regional level, a decision-making tool mitigating the seismic damage for future events is needed. This paper aimed to propose a rapid decision-making tool promptly estimating seismic damage with simple information and determining a retrofit scheme using a pre-developed extensive database, i.e., multi-dimensional structural parameter surfaces. The multi-dimensional surfaces were created using a simplified modeling approach with five structural parameters: period, strength ratio, and ductility controlling failure modes as the input, and peak inter-story drift ratio and demand-to-capacity ratio as the output. The proposed methodology was validated using a finite element model for the piloti-type building structure with a soft-story mechanism. The seismic responses detected from the multi-dimensional surfaces have a slight difference from those of the numerical model. Nevertheless, the rapid tool predicted a reasonable agreement with performance evaluation from the finite element simulation. In addition, the rapid tool provided feasible retrofit options to meet target performance using brief structural information. Due to its simplified process, the proposed tool can be implemented to the regional seismic assessment for the residential areas where the piloti-type building structures were highly concentrated. • Seismic vulnerabilities to piloti-type buildings highly concentrated in urban areas due to their vertical irregularities. • Extensive database from simplified numerical models reproducing the seismic vulnerabilities of the piloti-type structures. • Development of a database-based tool for regional seismic damage assessment of the piloti-type buildings. • Validation of the proposed tool with finite element simulation of a vertically-irregular building structure. • Establishment of retrofit schemes for piloti-type building structures with brief structural information. [ABSTRACT FROM AUTHOR]

• A new rapid tool to determine multi-hazard performance and retrofit scheme. • Artificial neural network models developed for rapid performance evaluation. • A framework for combining seismic and blast performance limits using the ANN models. • Demonstration of the rapid tool to select an effective retrofit scheme under multi-hazards. Non-ductile reinforced concrete building frames have seismic and blast vulnerabilities due to inadequate reinforcement detailing resulting in premature failure. One option to mitigate these vulnerabilities is the installation of a retrofit system on susceptible structures. However, differences in code-defined performance limits depending on loading type may result in a non-conservative retrofit design under multi-hazard loads. This paper presents a rapid tool for multi-hazard assessment and mitigation for the seismically-vulnerable building frames using artificial neural network models, which can rapidly generate large datasets. Using the models, energy-based performance limits for multi-hazard loading are derived, and a rapid decision-making approach for the retrofit design is developed under seismic and blast loads. [ABSTRACT FROM AUTHOR]

Non-ductile reinforced concrete building structures built before the 1970s have been significantly damaged and collapsed under man-made disasters (e.g., blast loads) due to their inadequate column details. The structural deficiencies can be mitigated by a fiber-reinforced polymer jacketing system. This research investigated the blast performance of a low-rise non-ductile building frame strengthened with the jacketing system. Based on the investigation, a retrofit scheme was established to mitigate the blast-induced damage and maximize the effectiveness of the retrofit system. The retrofitted models varied with the main parameters of the retrofit system associated with the confinement effect and flexural stiffness, and blast simulation was performed under various loading scenarios. The retrofit effect was examined in terms of confinement and stiffness ratios. Since the effects of the retrofit parameters on the blast performance depend on the blast loads, the retrofit scheme needs to be established in terms of expected blast loading scenarios. [ABSTRACT FROM AUTHOR]

Past seismic events have led to the premature failure of many existing seismically-vulnerable reinforced concrete building frames due to their inadequate column details. To ensure the ductile behavior of the non-ductile building frames, a hybrid retrofit system combining high-strength near surface mounted bars (flexural retrofit) with carbon fiber reinforced polymer sheets (shear retrofit) can be installed to the seismically-vulnerable columns. This study presents the experimental dynamic assessment of the non-ductile building frames retrofitted with the hybrid system. To prevent the column shear failure due to the flexural strengthening, a two-stage design procedure for the hybrid retrofit system was proposed. The full-scale dynamic testing was performed on the retrofitted test frame to realistically measure dynamic responses and quantify the retrofit effects. The hybrid retrofit system reduced the peak inter-story drift of the first-story columns by about 25% and their hinge rotation by approximately 76%. Additionally, the retrofit system can uniformly distribute the damage or drift over the entire structure, i.e. mitigation of soft-story mechanism. [ABSTRACT FROM AUTHOR]

• Investigates the effect of various connectors on the seismic performance of the system. • Input accelerograms matched the response spectrum for nonstructural components. • The specimen using the H-beam frame connector had the highest seismic performance. • Direct connectors helped the system dissipate seismic energy efficiently. • Connectors with large pole lengths are not recommended in this system. The seismic performance of the lighting systems is rarely reported in the literature, although previous studies indicate that they could be vulnerable during an earthquake. This study investigated the effect of various connectors on the seismic performance of an innovative wireway vibration attenuation system for raceway light fixtures using shaking table tests based on ICC-ES AC156 standard. The floor spectrum was created, and its compatible floor motion time history was employed as the input motion. Four typical prototypes were prepared with connectors suitable for mounting on a variety of structural components, including ceiling, H-beam frame, wall, and beam and column. The test results demonstrated that the specimens with the direct connectors (Wall and H-beam frame) had excellent seismic performance, 1.4–2.0 times higher than those with the pole connectors (Ceiling and Beam-column). Therefore, the direct connectors are proposed for this innovative system to decrease the danger of system failure during an earthquake. [ABSTRACT FROM AUTHOR]

• A total of 335 mix proportions were conducted to generate the data. • The range of compressive strength was determined from 5.44 to 67.86 MPa. • Compressive strength of geopolymer concrete was predict using DNN and ResNet approaches. • Performance of machine learning approaches was evaluated with metric measurements. In this research, two different machine learning approaches are proposed for predicting the compressive strength of fly ash based geopolymer concrete. Experimental work with a total of 335 mix proportions were conducted to produce the data for training and validating processes. In the proposed models, the amount of fly ash, water glass solution, sodium hydroxide solution, coarse aggregate, fine aggregate, water, concentration of sodium hydroxide solution, curing time, and curing temperature were considered as nine input variables, while compressive strength was the output feature. The performance of the machine learning approaches was evaluated using a set of three metrics, including correlation coefficient (R), mean absolute error (MAE) and root mean square error (RMSE). Good correlation between machine learning models and experimental results was obtained. The proposed models can be employed to build a standard mix, and for designing the mix proportions of fly ash based geopolymer concrete. [ABSTRACT FROM AUTHOR]