Oct'21
The IUP Journal of Structural Engineering
Focus
The second paper, "Analysis and Design of an RC Cable-Stayed Bridge", by Aishwarya Sadarjoshi, Sandhyarani Kalarakoppa, R Shreedhar, Pavan V Gudi and Nitin Deshpande, designs a cable-stayed bridge over a river to connect Ghodageri and Avargol villages. The authors have discussed the possibility of arch bridge. They considered only stone arch bridge and ruled it out for this site as it is not suitable for the span. Probably, the authors could have explored multiple span arch bridges of stone for this site. There are several such bridges still existing in India. Further an arch bridge is more suitable for a long span. It can be designed using steel too.
A very long arch bridge of steel is being built on Chenab River in Jammu for rail traffic. As far as cable-stayed bridge is considered, it is an aesthetically pleasing structure, and now several have been built successfully in the country. The paper designs a structure which is strong and light too with highest strength to weight ratio. This cable-stayed bridge in the example has an RCC deck with slab and beam. These slab and beam are further supported by high tensile cables attached to two pylons. One end of the cables is connected directly to the deck slab and another end is tied on the pylon. Harp type cable arrangement is chosen here. Pylon design could have also been shown. The whole design work has been done manually, which is commendable. A cable-stayed bridge is a highly indeterminate structure, and these days, more powerful software is available to analyze and design such structure.
The third paper, "G+40 Tube in Tube RC Frame Structure in Different Seismic Zones: A Comparative Analysis", by Shubham S Mutagekar and V D Gundakalle, studies the response of RC structure with tube in tube construction in various seismic zones. The study used the revised IS code 1893 Part 1 (2016) for analyzing a 114 m tall tube in tube structure. The structure is further provided with diagonal bracings to compare the response obtained with only tube in tube frame. A tube building is considered to be quite efficient in resisting lateral forces also. The objective is to plan and analyze one 41-storey RC frame tube in tube structure using Auto Cad and Staad Pro V8i SS6 software. These software are quite powerful and a very useful tool to the designers. Further, the study has compared displacement, storey drift, base shear in different seismic zones of the country. It is observed that tube in tube system in tall buildings will provide strong lateral resistance as compared to moment resisting frame. There is reduction in displacements and storey drift too. The study found that with selected properties of beam, columns and tube, the base shear is reduced up to 25%. Further, the base shear for tube in tube structure with bracing systems shows slightly less reduction than compared with only tube in tube structure.
The fourth paper, "Strengthening of Open Ground Storey Building Frame Including Soil-Structure Interaction", by Deepa Sunil Mahalkari and Hemant Sonawadekar, improves structural performance of Open Ground Storey (OGS) buildings under seismic excitation, including the interaction effects. In the study, efforts have been made to consider various strengthening schemes to improve performance. Six different models are considered for a G+4 storey building and analyzed using ETABS software. For analysis, brick wall infills are considered. The results indicate that a bare frame building without any infill wall had flexural failure. The OGS frame failed in flexure and in shear mode of RC members. A fully infilled frame had damages after failure of brittle infills in all storeys. The code recommended strengthening scheme by considering higher design forces in first storey does not improve lateral load resisting capability. Addition of extra columns in the first storey substantially improves performance. Introduction of bracings reduces the interstorey drift.
The last paper, "Dynamic Analysis of Single-Layer Reticulated Geodesic Dome:
A Literature Review", by Roopa M, H Venugopal and C M Ravi Kumar, reviews published work on dynamic analysis of dome. A geodesic dome is a thin shell structure made out of triangles connected together to form a true sphere. Papers have been published on seismic effects on such domes and efforts have been made to study such publications. It included the work on dome by theoretical approaches, Finite Element Analysis (FEA) packages/software tools, time history analysis, response spectrum method, static push over analysis and experimental tests. Based on the review, the authors have concluded that geodesic dome consists of segments of triangles with less utilization of raw materials. It is safe against earthquake vulnerability as compared to flat roofs. It is observed that several researchers have used SAP2000 and ABAQUS software for its analysis, as these packages are quite user-friendly and many design alternatives can be included.
Consulting Editor
Evaluation of Magnification Factor for OGS Buildings with Combined Effect of Flexure and Torsion
Multi-storey buildings are in high demand owing to demographic growth and also because open ground floor parking and a reception hall are unavoidable. Usually a framed structure, including a soft storey at the bottom, is tested by neglecting the rigidity of infill to study the conduct of Open Ground Structures (OGS). Besides soft storey, asymmetric constructions are also inevitable owing to functional diversity and architectural desires. Therefore, the shear force and Bending Moment (BM) of the columns positioned on the ground floor must be amplified according to Indian Norms. Recommendation for Magnification Factor (MF) as per IS:1893 (2002) is 2.5, and this MF must be applied to the BM and shear force of ground floor columns. Due to the combined impact of soft storey and torsion, attempts are made to assess the MF in the current work. The torsional reaction of structures under seismic excitation is due to an uneven configuration, resulting in a non-symmetrical distribution of mass and rigidity. A linear Response Spectrum Analysis (RSA) assessment is performed on five floor structure and imposed with a seismic excitation of 5%, 10% and 15%. Comparisons are made between regular eccentric structure and structures with varying eccentricity. It is deduced from the assessment that the MF suggested by IS: 1893 (2002) of 2.5 is high. And there is no need to apply MF for beams, as it will increase the seismic demand in columns.
Analysis and Design of an RC Cable-Stayed Bridge
Bridges have played an important role in the development of earliest civilizations. APJ Abdul Kalam, the former president of India, believed that "physical communication between two places paves way for development". This belief inspired great scholars across the world. One of them was Girish Bharadwaj, also called 'Sethu Bandhu' and 'Bridgeman of India', for building around 127 low-cost and eco-friendly bridges in remote villages across India. He was conferred the Padma Shri award in 2017. One of the longest bridges built by him was the one connecting the villages, Ghodageri and Avargol. The bridge spanned about 210 m over the river Ghataprabha. It enhanced the beauty of the river surrounded by nature, and hence the place is well recognized as a tourist spot. Due to floods that occurred in the year 2019 in Karnataka, devastation of the newly constructed bridge happened. As the bridge served the purpose of providing passage over the river, people residing there face problems of transportation. Therefore, the paper presents a design of an RC cable-stayed bridge to fulfil the purpose economically.
G+40 Tube in Tube RC Frame Structure in Different Seismic Zones: A Comparative Analysis
Tall structures have amazed the modern world from early stages. Tall buildings have been a great attraction for humans since the beginning of civilization, as evidenced by the pyramids of Giza, Egypt; the Mayan temples of Tikal, Guatemala; and the Qutub Minar of Delhi, India. Nowadays, there is a need for multi-storied buildings as the cities are getting overcrowded. In tall buildings, the lateral loads which act on the building resist the wind loads and earthquake loads by providing braced framing system. Bracing is widely used in tall structures; these are also called lateral load reducing system. Based upon the previous research, a G+40 RC tube in tube structure is analyzed along with a bracing system using the revised earthquake code IS: 1893 Part 1 (2016). The results like base shear, storey displacement and storey drift are analyzed and compared, and it has been observed that tube in tube structure without diagonal bracing system gave the best results in both X and Z directions for base shear, whereas the displacement slightly reduced after providing diagonal bracing for tube in tube structure in both X and Z directions for various zones.
Strengthening of Open Ground Storey Building Frame Including Soil-Structure Interaction
Open Ground Storey (OGS) buildings, which are vertically irregular, are open to damages under seismic activity as a cause of discrepancy of infill stiffness over the building height. The design procedure is generally based on fixed base condition neglecting the soil flexibility below the foundation, which adversely affects the building's seismic performance. The flexible base tends to reduce structural stiffness by augmenting its natural period. Though this interrelationship between the structure and soil is of great concern in the seismic analysis of OGS structures, no guidelines are available on Soil-Structure Interaction (SSI) in the Indian Standard Codes. Eventually, strengthening of OGS structure becomes vital in order to enhance the seismic performance of such buildings. The paper intends to improve the OGS building performance considering several strengthening schemes, including SSI. The behavior of fully infilled frame and difference in behavior of OGS frame with the provision of stiffer column, bracings and additional columns in the soft first storey are studied by carrying out the analysis in ETABS.
Dynamic Analysis of Single-Layer Reticulated Geodesic Dome: A Literature Review
The paper focuses on the works performed specifically for dynamic evaluation of single-layer reticulated geodesic domes, and several studies are discussed in brief. The Finite Element Analysis (FEA) software packages and analysis methods like time history, response spectrum and details about geodesic dome along with its geometric configuration are highlighted. The experimental assessments and methodologies are also discussed. The conclusions are drawn based on the research works carried out.