International Journal of Civil Engineering
Volume:19 Issue: 1, Jan 2021

This work studies a new design procedure to account for accidental torsion in buildings subjected to seismic ground motions. The procedure does not require a design accidental eccentricity and it is based on a simple amplification of design parameters obtained from the corresponding model without accidental torsion. The objectives of the study are to present and to evaluate the torsion design proposed procedure. Based on representative low-rise, reinforced-concrete building models subjected to a bidirectional earthquake ground motion, several scenarios of accidental torsion were simulated using the Monte Carlo method. In the first part of the study, elastic analyses of simulated models were carried out to obtain the amplification factor value (Fat). In the second part, nonlinear analyses were performed to evaluate the design proposal based on ductility demands. Main conclusions of the study are: mean values of ductility demands do not significantly change between the torsionally balanced (TB) system and the corresponding one with accidental torsion (TU with Fat = 1.0). However, these mean values decreased about 18% for beams and 16% for columns when the torsion amplification factor (Fat = 1.2) was used in the TU systems. As for peak ductility demands, the unbalance due to accidental torsion leads to increments close to 42% for beams and 54% for columns. On the other hand, the torsion amplification factor Fat = 1.2 reduces the peak values in 25%, approximately, for beams and columns of systems with accidental torsion. Main limitations of the study are: it is based on one bidirectional ground motion (with several incidence angles) and eight structural models.

This study investigates the mechanical and thermal properties of cement mortars incorporating two types of waste slags: ferrochrome (FeCr) slag aggregate was used as a replacement for sand at ratios of 25, 50, 75 and 100 wt%, and ground granulated blast furnace slag (GGBS) was used as a partial replacement for cement at a ratio of 25 wt%. Compressive strength, volume of permeable voids (VPV), drying shrinkage, and thermal conductivity tests were conducted after 28 days of curing. The microstructure characteristics were examined by scanning electron microscopy. The experimental results revealed that FeCr waste aggregates could satisfactorily replace natural fine sand in cement mortars up to 25 wt% without a remarkable degradation of compressive strength. Furthermore, increasing the replacement ratios of FeCr aggregates by over 25 wt% resulted in a noticeable decrease in thermal conductivity and an increase in the permeable void content of cement mortars. The increased VPV of FeCr slag-blended mortars led to a significant increase in drying shrinkage. The integration of GGBS with FeCr aggregates led to enhanced compressive strength and reduced VPV and drying shrinkage, thus contributing to an improved microstructure.

Electrical resistivity is widely used to monitor the durability of concrete structures. However, the results obtained can be misinterpreted due to the effect of several parameters on the test. Therefore, the effect of six parameters on the electrical resistivity was investigated in this article. The studied parameters were (1) the thickness of the concrete cover; (2) the contact with the concrete mold; (3) the concrete aging; (4) the chloride presence; (5) the type of cure and exposure; and (6) the position of the equipment regarding the reinforcement direction. Tests were performed on aged non-reinforced concrete specimens (5 years old) and freshly casted specimens. The results showed that variation in the thickness of the reinforcement covers from 1.5 to 3.0 cm affects the electrical resistivity measurements, independently of the w/c ratio. The contact of the concreting mold with the specimen did not influence the values of electrical resistivity, independently of the w/c ratio. The effect of the chlorides incorporated into the mass of the concrete during casting is not significant on the electrical resistivity at 28 days. The electrical resistivity was 13.2% higher in specimens cured in a moist chamber, compared to curing in an uncontrolled external environment. The electrical resistivity was no longer influenced by the steel at a minimum parallel distance of 8.0 cm. Measurements performed perpendicular to the bar were not affected. These results are very important for a better interpretation of the results of this technique.

This study focuses on proposing a novel mix design method giving emphasis to the durability of concrete and replacing cement with supplementary cementitious materials (SCMs) at certain percentages. It also includes band gradation of aggregate that merges fine and coarse aggregates to result in a single well-packed combined gradation. Two replacement levels (20% and 35%) of fly ash and three replacement percentages (20%, 65% and 90%) of slag by weight of cement were used to prepare a significant number of concrete mixes. Compressive strength, workability and durability of the prepared mixes were determined. Rapid Chloride Permeability Test (RCPT) was carried out for measuring durability of concrete. From the prepared mixes, it was possible to achieve 90-day RCPT value as low as 216-coulomb and 28-day compressive strength up to 46.5 MPa. Several contour plots were developed correlating the three mix design parameters (compressive strength, slump and durability) with cement and water contents. Finally, using the plotted contours, a mix design process has been organized into five simple steps that can easily be followed in order to proportion an optimized ratio of cement, aggregate and SCMs for preparing durable and economical concrete mixes.

In the present study, the effect of peak occurrence time and flood duration on the scour around the bridge pier installed in a sharply bended channel was investigated. For this purpose, several simple single-peaked hydrographs with the same durations and different peak occurrence times were produced in laboratory. In addition, hydrographs having two consecutive peaks with a steady flow discharge at the first peak and an unsteady-flow discharge at the second peak and vice versa were investigated. The flow velocity range began from incipient motion conditions and steeply increased to live bed conditions. In each experiment, the temporal variations of the maximum local scour depth were measured. In single-peaked experiments, by increasing hydrograph duration from 25 to 100 min, the maximum scour depth increased by 20%, and the progression of sediments along the downstream straight path increased by 150%. For hydrographs with two non-equal and the same duration peaks, at a constant discharge for the first peak and a decrease in the second peak discharge from 70 to 60, 50, and 45 (L s−1), the volume of the scour hole around the pier was decreasing 15, 40, and 60%. Its area fell by 10, 40, and 55%, respectively. When the rising and falling limb time of hydrographs were equal, the maximum sedimentation height increased by 2.7, 3.5, and 5 times, respectively by increasing test duration from 25 to 50, 75, and 100 min. 

This paper introduces a simulation–optimization method for addressing scheduling problems for shuttle freight trains (SFTs) in a shared railway corridor between a seaport and dry port. We use dispatching delays for scheduling the SFT trips so as to not disturb the existing scheduled regular train (SRT) paths. The method employs a multi-method microscopic simulation model and an optimization framework. A swarm-based optimization algorithm is used for finding the best dispatching delays to preserve SRT paths. The method is demonstrated for a railway corridor between the Alsancak seaport and a close-distance dry port. The railway corridor is modeled using a simulation model considering single and double railway tracks, stations, and schedules. By running the simulation–optimization, the SFT freight transport capacity and the quality of the SFT and SRT operations were compared using key performance indicators (number of completed trips and station stops, average trip delay, and average station delay) addressing the throughput and punctuality after the application of dispatching delays. The results show that, by preserving the existing SRT paths, freight transport capacity decreased by 11.1% (from 18 to 16 completed SFT trips) and 13.8% (from 36 to 31 completed SFT trips) for single and couple SFT scenarios, respectively. The methodology also decreased the average SFT station delays by 45.2% and 45.6% for the single and couple SFT scenarios comparing with the unoptimized SFT trips. However, the number of SFT station stops increased by 12.5% and 57.1% for the single and couple SFT scenarios for prioritizing the SRTs. Also after the optimization, the average SFT trip delays decreased by 30.7% and 0.58% for the single and couple SFT scenarios. This study successfully demonstrates that the proposed method can be used for scheduling the SFT trips inside a congested railway corridor and can be implemented as a capacity assessment tool for cyclic SFT service using a series of key performance indicators addressing throughput and punctuality.

The application of building information modeling (BIM) in the Vietnamese construction industry is still in its early stage, both in perception and practice. This leads to a necessity of an effective legal system and standards for BIM implementation. In this study, a systematic literature review was conducted, including relevant references from journals, conference proceedings, and graduate-level theses published from 2008 to date, to identify legal issues and their potential solutions. The identified legal issues were analyzed in relation to the Vietnamese construction sector, and then verified and assessed through a survey. Both Friedman test and Wilcoxon signed-rank test were applied to rank the BIM legal issues. The findings show that the most significant barrier in adopting BIM is the lack of consistency and participation of stakeholders in the BIM implementation process. Expert interview was conducted to evaluate the solutions for BIM legal issues in the Vietnamese construction market. Through surveys and expert interviews, various legal issues, risks, and barriers associated with the adoption of BIM in the Vietnamese construction industry were identified and addressed. Information about BIM contract awareness and experiences was also revealed, which would help verify the risks affecting the parties in a BIM-inclusive construction project, as well as those affecting information exchange and intellectual property rights in Vietnam. Finally, the paper suggests a set of critical success factors and a contractual framework that would lead to a successful BIM-inclusive construction contract in Vietnam.

Pooled step cascade weirs are hydraulic structures that are preferred over ordinary weirs due to their application on steep slopes and to their effectiveness in obtaining water aeration. However, these structures are subject to failure due to scour being initiated downstream, or to breakdown due to the high energy of impinging water. In this paper, an experiment was presented to study the effect of the number and ratio of holes in weirs to improve energy dissipation. To improve energy dissipation, cascade weirs with different configurations of openings were proposed. Furthermore, a sluice gate at the upstream of a cascade weir was proposed as a new technique to increase energy dissipation and reduce scour at downstream. Ten models of pooled step cascade weirs (nine models with different hole configurations and one with a sluice gate upstream), in addition to the ordinary weir, were constructed to investigate the effect of the sluice gate and holes on energy dissipation; the range of each type of flow (nappe, transition, and skimming); the relevant Froude number; and the ratio of water depth to critical depth over pooled step cascade weirs. To implement this, the ratio of holes to the area of the weir were between 0 and 21.22% and the number of holes used were one hole, two holes, and three holes. The results concluded that the best method to obtain maximum energy dissipation was putting a sluice gate at the upstream of a solid pooled step cascade up to a discharge of 2.0 l/s. The most effective ratio of holes to weir area was 7.15% at the minimum Froude number when the discharge exceeded 2.0 l/s. Moreover, the ratio of upstream water depth to critical depth decreased with increasing discharge. The nappe, transition, and skimming flow types were increased more on a pooled stepped cascade weir of 7 mm opening diameter with three holes (ratio of 7.15%) than the other models. The Froude number decreased as the hole numbers increased at high discharges for the pooled stepped cascade weir, especially with the hole diameter of 12 mm. Some empirical equations were established to represent the relation between the upstream head and discharge for each case.