Progressive collapse analysis of RC buildings subjected to seismic loads
Harinadha B. Raparla and R. Pradeep Kumar

Earthquake performance of Reinforced concrete bare frame has been well documented in the past.  Also, damage patterns in reinforced concrete frames during the past earthquakes have been extensively studied. However, more recently, several destructive earthquakes, including the 1999 Athens (Greece) earthquake, the 1999 İzmit and Düzce earthquakes (Turkey), 1999 Chi Chi (Taiwan) earthquake, 2001 Bhuj (India) earthquake, and the 2003 Boumerdes (Algeria) earthquake, have given more insights to performance of RC frame constructions. In order to understand the complete behavior of RC frame, it is required to study the performance from no loading condition till the complete collapse. In this paper, a set of four bare frames designed as per Indian Standards are considered. All the frames are subjected to Northridge earthquake ground motion. Newly developed numerical model called Applied Element Method (AEM) is considered for analysis. Initially, the linear analysis is carried out and the results were compared with commercially available software. Later, progressive collapse analysis is performed. Collapse process of each bare frame is discussed in detail.

Study on stress corrosion cracking of prestressed strand in different environments
J.D. Rathod, B.S. Trivedi and A.R. Sankhat

In this paper an attempt has been made to study the effects of stress corrosion cracking (SCC) phenomena in high strength steel, typical of those used as tensioning tendons in prestressed concrete, in several corrosive environments. Chlorides and sulphates present in the concrete affect corrosion of prestressed strand which in turn influence long term performance of the structure.  As a part of the experimental work, stress bench of 21ft. length was prepared with two end-bearing plates each having 18 numbers of holes of 5mm diameter which allow the strand of 4 mm diameter to pass through it. The three different sets (each set having six numbers of strands) of stressed strands are kept in acrylic buckets of three different corrosive environments like Sodium Chloride (NaCl), Ammonium Thiocyanate (NH4SCN), Sodium Sulphate (Na2SO4) with their respective concentration recommended by FIP (Federation International de la Prestressing). Effects and changes in surface of strands are studied by keeping the stressed strands in wet and dry cycle of 36 hrs. for 45 days. Stressed strands in different corrosive environment show different rate of loss in its cross sections based on its severity. For further detailed investigation, Scanning Electron Microscopy (SEM) images and EDS for chemical analysis turned out to be very helpful to observe clear changes in loss of few significant metals in particular sample of strand before and after the test performed.

Computation of fundamental time period of concrete gravity dam - A parametric study
Deepak Pal, Syed Samiullah, Vinay Kumar, Hari P. Samal and Milan Bandyopadhyay

A parametric study is conducted with the objective to find the dependency of fundamental time period of the concrete gravity dam on its base width, height and slopes on upstream and downstream faces. Two dimensional studies are conducted on 353 geometric variables of dam with rigid foundation using general purpose finite element software. Time period calculated for different alternatives of the dam are compared with those calculated using empirical equation of Indian Standard and as per published literature. Results obtained through different methods are in good agreement when base to height ratios are in the range of 0.7 to 0.8.

A study on deterioration of reinforced cement concrete structures in Mumbai
Suresh C. Pattanaik, E. Gopalkrishnan and Sanjaya K. Patro

The deterioration of reinforced concrete structures not only depends on the microstructure of the concrete but also on severe exposure conditions in a particular environment. Reinforced cement concrete structures are exposed to the deteriorating effects of operating and natural environments – the single or combined effects of which have a bearing on safe functioning of the structure. In marine environment, the risk of corrosion on outdoor structures is very high. These effects result in age-related degradation of reinforced concrete structures while other reasons for degradation emanates from improper engineering of the structure. The durability of the structures is always a challenge to the designer for getting the desired service life. The performance of a structure in a particular exposure condition is a function of time and is related to durability and deterioration. Deterioration is the opposite performance of durability and can be taken as a performance problem. This paper discusses the various mechanisms for degradation of reinforced concrete structures in marine environment with some practical case studies of chemical deterioration of concrete structures in Mumbai, India.

Estimation of long-term prestress losses of box-girder bridge span using the prestress loss models in Indian and International codes of practices and comparison with field measurements
P. Kamatchi, B. Dhayalini, K. Balaji Rao, S. Saibabu, S. Parivallal, K. Ravisankar and Nagesh R. Iyer

In this paper, an attempt has been made to estimate the long-term prestress losses of an existing prestressed concrete box girder bridge span using  the models proposed in International and Indian codes of practices  viz., Indian Standard code of practice for prestressed concrete (IS 1343:2012),  Code of practice for Concrete Road Bridges (Indian Road congress IRC:112-2011), Eurocode 2:Part 1-1:2004, American Concrete Institute (ACI 209R-2010), American Association of State Highway and Transportation Officials (AASHTO LRFD 2007) and  Precast and Prestressed concrete Institute (PCI 2004).  Comparison of estimated losses with the field measurements indicate IRC 112-2011 and IS 1343:2012 provisions to be conservative.

 

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