Nepal Journal of Civil Engineering

Implications on the Utility of NBC 205:2012 due to the Revision of NBC 105:1994

Wed, 10 Apr 2024 00:00:00 +0545

Nepal published its own seismic design code Nepal National Building Code NBC 105:1994 for seismic design of Building in Nepal in 1994 which has been recently revised to NBC 105: 2020. However, the implementation of these seismic design codes for the design and analysis of low-rise residential buildings is a challenging task for a mid-level technician. As a result, NBC 205 was constituted with a motive to provide ready to use dimensions for residential RC structure and to facilitate pre-engineered construction for effective time utilization. This study focuses on the comparison of both revised and existing seismic design codes for the low-rise buildings, which are modeled to match the criteria prescribed in NBC 205. Five different models were analyzed using FEM tools and their structural responses like inter-storey drift, base shear, displacement, beam column ratio, time period, dimension and reinforcement were checked and collated to suggest appropriate alteration on column sizes and reinforcement prescribed by NBC 205 to meet the structural demands and design provisions of revised NBC 105:2020. Increase in sizes and reinforcement of column were observed and recommended to meet the increased structural demand.

Numerical evaluation of centrifuge tests of shallow foundation on liquefiable soil

Dristi Lamichhane, Patrick Staubach, Jan Machaček — Wed, 10 Apr 2024 00:00:00 +0545

Earthquake-induced liquefaction is one of the major geo-hazards to cause damage to engineering structures. There is an emerging need for a thorough investigation of numerical tools to predict the behavior of liquefiable soils. This paper studies the ability of numerical models to predict the behavior of fully saturated soil under earthquake loading. A numerical back-analysis of centrifuge tests of light and heavy shallow foundations resting on fully saturated soil subjected to earthquake loading is performed using a sophisticated constitutive soil model, the SANISAND model. Different hydro-mechanically coupled finite element formulations are used to consider effects resulting from the interaction of solid grains, fluid, and foundation, including inertia forces. The simulations are performed with either u-p elements or u-p-U elements, where u, p, and U denote the solid displacement, pore pressure, and fluid displacement, respectively. The results show that despite some discrepancies between the simulations and centrifuge test results, the numerical models capture the magnitudes and trends of displacement and deformation mechanisms reasonably well. Additionally, the u-p and u-p-U element formulations led to similar simulation results, showing that the relative acceleration between the pore water and the solid has negligible influence on the predicted deformations even when the frequency of the signal and hydraulic conductivity are high.

The Optimization of river diversion structure and cofferdam in Sunkoshi –Marin diversion scheme.

Mukesh Raj Kafle — Wed, 10 Apr 2024 00:00:00 +0545

This study evaluates and optimizes the temporary diversion scheme with cofferdam in Sunkoshi-Marin diversion scheme. The optimization ensured economic viabilty and safety during construction. Two river diversion options (i) surface diversion and (ii) tunnel diversion were analysed and compared. Numerical analysis in HEC-RAS was carried out to calculate the requirement of channel width and depth of flow for floods varying from 2 to 20 years return period. The cost of different diversion options was calculated to optimize the surface option and compare with the sub-surface option. The cost of the diversion works was compared with the cost of loss due to the flooding of structures for the optimization of protection works. The analysis showed the cost of diversion works corresponding to the 10 years return period diversion flood well balances the loss due to flooding. The cost of diversion by tunnel is more than three times of surface diversion option. The study recommends surface diversion option as the optimal solution during the construction of Sunkoshi-Marin diversion headworks.

Signal optimization to improve traffic conditions: A case study of Satdobato and Gwarko intersections, Kathmandu Valley

Wed, 10 Apr 2024 00:00:00 +0545

This study introduces a methodology for assessing intersection performance and examining various signalization strategies. The methodology was applied to analyze and optimize traffic signals at two intersections in Kathmandu Valley, namely Satdobato and Gwarko. Micro-simulation software ’SIDRA Intersection 9.0’ was utilized to model these intersections, with calibration and validation performed using field data. The performance assessment primarily focused on average delay and back of queue length, followed by network evaluation. The current operational performance at Satdobato showed an average delay of 226.5 seconds per vehicle, while Gwarko had an average delay of 201.1 seconds per vehicle. Sensitivity analysis identified the basic saturation flow as the most critical parameter for both intersections. Optimized signal phasing, the leading right-turn configuration with optimal timing with a cycle time of 100 seconds for Satdobato, and the existing scenario with optimal timing with a cycle time of 70 seconds for Gwarko resulted in reduced average delays of 51.8 and 52.5 seconds per vehicle, respectively. Network analysis for the combined intersections led to a back of queue length of 606 m, slightly higher than the 578.9 m observed for the optimized individual intersections. Despite substantial improvements with optimized signals, signal coordination appeared to be ineffective in this particular case.

Study of Sugarcane Bagasse Ash as Replacement of Cement in Soil Stabilization

Bhim Kumar Dahal, Deepak Raj Paneru — Thu, 04 Apr 2024 00:00:00 +0545

This study examined the binder potential of sugarcane bagasse ash (SBA) alone (2-16%), a by-product of agro-industries, cement binder alone (2-12%) and partially replacing 6% cement content with bagasse ranging 10 – 70% by weight of cement in soil stabilization considering Atterberg’s limit, compaction characteristics and unconfined compressive strength (UCS) at 3, 7, 14, and 28 days curing period after the specimen is prepared using Harvard Miniature test apparatus. Test results shows that both cement and bagasse ash reduce the plasticity of soils. However, the decrement in plasticity of soils is more in case of cement than bagasse ash. In the case of partial replacement, the plasticity of soils decreases up to 20% replacement and then increases gradually. The compaction test showed that Optimum moisture content (OMC) increases, and Dry Unit Weight (MDW) decreases as compared to original soil sample at all binder content. The UCS increases with all cement content. However, in the case of SBA it is so only up to 8% ash content then decreases. The UCS showed that bagasse ash stabilizes the soil; however, it is not as effective as cement as binder even that of lowest cement content 2%. The maximum UCS value increases by 2.58, 9.66 and 9.89 folds the original soil sample at 8% bagasse ash content, 6% cement content and 6% cement content replaced by 20% bagasse ash by weight of cement respectively. Thus, it can be concluded that, the bagasse ash cannot fully replace the cement, however it can partially replace the certain cement content without compromising the strength characteristics.

Airport Choice Modeling between Tribhuwan International Airport and Nijgadh Airport

Nishub Luitel, Pradeep Kumar Shrestha, Ashok Kumar Shrestha — Wed, 10 Apr 2024 00:00:00 +0545

An airport choice model was created to understand how people decide between Tribhuvan International Airport (TIA) and the proposed Nijgadh International Airport. Three things were considered: how long it takes to get to the airport, how much it costs, and if there are any announced delays. Data was collected from passengers at TIA during check-in, and a method called binary logistic regression was used for analysis. The results showed that the most important factor in choosing an airport was the announced delay. While the time and cost to get to the airport also mattered, they didn’t have as much impact. This study provides insights into what matters to international travelers when choosing an airport. It suggests that reducing delays could make an airport more appealing to passengers.

The Pile-Raft Interaction Effect for Building Structures

Rijan Shrestha, Ram Chandra Tiwari — Wed, 10 Apr 2024 00:00:00 +0545

This paper makes the study about the combination of the pile and raft foundation since it is becoming more and more popular as a foundation system for the multi story building. In this type of foundation the load will be shared among the raft and pile which may not be equal. This paper discusses the pile settlement, load carried by the foundation where the structural load is shared by the the piles and sub-grade soils beneath the raft. This study is done for the site located at Balkhu, Kathmandu where new commercial building is about to be made. The building is of 10 story with floor height of 3m. This study assessed the some of the characteristics and the effect caused in the super-structure and the sub-structure. To make modeling of such cases easier, the Mohr-Coulomb constitutive soil model was included in the PLAXIS 3D computer program. The result are presented including the area affected by the construction of the structure and the effect caused due to the consideration of different boundary condition. The foundation capacity mainly depends upon the bearing capacity of the soil underneath at the site. The soil data of the site is obtained from the soil investigation report for the site which was done by digging seven borehole and the information from the report is used for the soil modeling process.