Construction Technologies and Architecture Vol. 11

Abstract: Austenitic stainless steels tend to form chromium depletion zones during welding. The chromium combines with available carbon around the grain boundaries to produce chromium-deficient areas, thus becoming susceptible to intergranular corrosion. The sensitization phenomenon of 304 stainless steel during gas tungsten arc welding (GTAW) process has been investigated. In this experiment, there were four welded samples observed. Two welded samples were cooled in air and cooled in oil immediately after welding, respectively. Meanwhile, another two welded samples were normalized by heated to 800 and 900 °C and held for 0.5 h before cooled in air. The welded samples were analyzed using optical microscopy, scanning electron microscopy and energy dispersive microscopy (SEM-EDS), and a Vickers hardness testing machine. The results show that normalizing affects significant changes in the microstructure due to the sensitization phenomenon. It can be seen that there is more carbide deposition in the welded sample with cooled in air and welded samples which normalized by heated to 800 °C and 900 °C and held for 0.5 h before being cooled in air. Meanwhile, the sample that was cooled in oil immediately after welding showed fewer chromium carbides. Normalizing the welded samples to 800 and 900 °C and holding it for 0.5 h before cooling in air triggers the sensitization process. Sensitization looks less occur in 304 stainless steel welds which were rapidly cooled in oil.

Abstract: The effect of heat treatment process on the microstructure and hardness of train wheel material was investigated. The railway wheel material was prepared by a casting process from used train wheel and followed by heat treatment processes namely normalizing, flame hardening, and tempering. The normalizing process at a temperature of 850 °C with a holding time of 120 minutes followed by air cooling has resulted in hardness of 24 HRC. The flame hardening process at a temperature of 800 °C with a holding time of 1 minutes followed by water quenching has resulted in hardness of 57.33 HRC. The tempering process at a temperature of 500 °C with a holding time of 60 minutes followed by air cooling has resulted in a final surface hardness of 34 to 37 HRC that complies with the standards.

Abstract: This research aims to review the physical properties of Lightweight Cellular Concrete (CLC) bricks with the addition of Labuhan Batu Selatan red sand. CLC bricks have the advantage of being lightweight and larger in size, which can expedite the construction process. CLC bricks are made by adding air bubbles/foaming agents to the mortar mix as an expander to produce lightweight bricks with a lower material composition. It is crucial for the air bubbles to maintain their shape during the mortar curing process without causing any chemical reactions. In this study, lightweight bricks were made by experimenting with various combinations of red sand and river sand, with variations of 0% red sand and 100% red sand, using the Cellular Lightweight Concrete (CLC) method. The research method employed was experimental, testing the physical properties of CLC lightweight bricks, specifically density and compressive strength, in accordance with the SNI 03-6825-2002 standard. As a result, with the addition of red sand in the production of CLC lightweight bricks, the density falls within the lightweight brick category, but it does not significantly improve the compressive strength of the lightweight bricks. This is because the CaCO3 (calcium carbonate) content in the CLC lightweight brick mix has the highest intensity, causing the bricks to become brittle. Therefore, this research suggests paying more attention to the mixing and blending processes of the materials to achieve a more uniform distribution.

Abstract: Earthquakes cause deformations in structural elements which then lead to interstory drift and probability of collapse in building structures. Incremental Dynamic Analysis (IDA) will obtain a graph containing the Response Spectral Acceleration (RSA) value for the maximum interstory drift ratio, which will then be used to calculate the probability of collapse using the Fragility Curve. The structure is planned to be located in Biak city on hard soil conditions with a 16-story two-dimensional SRPMK building model. Various ground motions scaled to the design response spectrum of Biak city with 2 different methods were used. Based on the analysis conducted, the average interstory drift value for RSA scaling (T1) is 0.33 meters and RSA scaling (T1 = 0) is 0.2 meters, both of which occur on the first floor of the building structure. The largest RSA value obtained through IDA for the RSA scaling (T1) was 1.63 g and the RSA scaling (T1 = 0) was 1.89 g. Through the Fragility Curve, the probability of structural collapse at an RSA value of 1.63 g is 0.99 and at an RSA value of 1.89 g is 0.75.

Abstract: On April 2-4, 2021, severe cyclone Seroja occurred in Kupang City, resulting in a landslide hazard. Landslide disaster management is essential for disaster mitigation. However, the susceptibility landslide map for the cyclone Seroja in Kupang City has not yet been done. In this paper, we map landslide locations using remote sensing. We used free remote sensing data. The data are Landsat 8 imagery, Digital Elevation Model (DEM), and rainfall. To create a landslide map in Kupang City, we overlaid three maps. Those are landcover, slope and rainfall maps. We created a landcover map using the Landsat 8 imagery. The landcover types were classified using the Supervised Classification method of Support Vector Machines (SVM) in the QGIS software. Each land cover type was determined based on training sites taken in the field using GPS. DEM was used to create a slope map. We used the accumulative rainfall data for three days to map the rainfall. For data validation, we took GPS points from the landslide locations. The study result shows a landslide map in Kupang City after cyclone Seroja. This work informs that remote sensing can be used to determine the location of landslides in inaccessible areas. Remote sensing can also be used to map landslide areas with a limited budget and limited data.

Abstract: Tarutung is a geothermal potential region and has relatively high seismicity due to the Sumatra fault system and young arc volcanism. There were many recorded significant earthquakes occurred in Tarutung. The seismic activity proves that a good understanding of the Tarutung tectonics is necessary. This research aims to study the tectonic setting and seismic activity of Tarutung area. In this study, we used Fast Marching Method (FMM) to relocate hypocenters using the arrival time of P-wave data. This data from temporary seismic station network deployed around Tarutung and Sarulla. The seismic station network consists of 42 short-period stations that deployed in May 2011 and continued to record 10 months of seismic activity. The relocation process used global velocity model of AK135, modified AK135, and local velocity model. The results show differences in terms of hypocenter relocated using each model. By analyzing the relocated hypocenters, each result can be used to represent the crustal seismic activity and tectonic settings of this region. The Sarulla region is on the Toru fault with a vertical linear distribution of earthquakes with a dip of 90⁰. The distribution of earthquakes is more spread out in the Tarutung area, which is a graben area. This is the result of the third velocity model with a residual travel time is 934.07 milliseconds.

Abstract: Landslide is a natural disaster in Indonesia, especially in the Aceh province, with its geological complex, high rainfall, and topography. The high-intensity landslides have occurred in Jantho and Lamno, located in the Northern part of Aceh, with high development costs of road infrastructure. Therefore, it is necessary to map the potential of landslides along the Jantho – Lamno road as disaster mitigation in the future. The research uses a digital elevation model (DEM) that applies slope, aspect, hill shade, curvature, elevation and geological observation to study the landslide probability. The DEM analysis shows the distribution of terrain with varying elevations of 300 – 1,200 m.a.s.l and slope characteristics with 10 – 50 degrees variations. Apart from that, curvature and aspect analysis describe the direction of slope reduction, which is more dominant towards the side of public infrastructure. Analysis of the four data distributions shows that the south side area has a large landslide potential. On the other hand, slope data slices at four locations could interpret landslide potential well. Based on data processing, we conclude that comparing DEM and geological observations is considered effective as a fast and economical method of mapping landslide probability, especially in tropical areas and high topography that is difficult to access.

Abstract: Geothermal is a very expensive investment industry. Therefore, it is necessary to map a geological structure in the sub-surface, i.e., faults, and rock formations that control volcanic hydrothermal systems to reduce investment risk in the exploitation of geothermal. On the other hand, the hydrothermal system aims for flow paths connecting reservoir wells for fluid production. The Jaboi Volcano, with an estimated 80 MWe located on Weh Island, Indonesia, has been planned by the government to develop electrical energy, where the excess energy will be exported to Banda Aceh via undersea cables. We use global gravity model plus (GGM+) in a resolution of ~230m/px for mapping the geological structure of Jaboi volcano. Based on GGM+ data analysis, the Bouguer anomaly data shows low gravity values in volcanic areas, namely 46 – 69 mGal. These data only represent rock density values with low density in geothermal areas. We also calculate the residual anomaly from the Bouguer data using the high-pass-filtering technique, wherein the volcanic area, several high-gravity anomalies (1 – 1.4 mGal) correspond to the Leumomate fault in the direction of NW-SE. The same pattern is also obtained in the area with a suspected Ceunohot fault in the SW – NE direction. This research demonstrates the optimization of gravity satellite that free access to be used in mapping geological structures in geothermal Jaboi. Finally, we conclude that GGM+ data is a very efficient and cost-effective technique to detect geological structures around the Jaboi volcano, which developing countries can use as a preliminary study for evaluating and exploring geothermal energy

Abstract: In this paper, we study convex quadratic relaxation in polynomial programming. The goal is to solve polynomial programs through quadratic reformulation with the factorization method. The quadratization of monomials of degree more than two is carried out by replacing each pair of factors of the monomial with auxiliary variables. In this paper, each pair of factors of a monomial will be considered. The quadratic program obtained is convexified by using eigenvalues. As a result, the quadratic reformulation involving all factors of the monomial strengthens the information of the polynomial function but increases the dimensionality of the variables significantly. The next work is to develop a strategy to reduce the dimensions of the auxiliary variables.