Simplified Method of Determining Torsional Stability of the Multi-Storey Reinforced Concrete Buildings

This article proposes a simplified method for determining the elastic radius ratio of the multi-storey reinforced concrete building. The elastic radius ratio is the benchmark parameter of the buildings in determining torsional stability during an earthquake. When buildings are torsionally flexible, the torsional component of seismic response amplifies the overall response of the building. Because of the numbers of simplified assumptions such as the adoption of the single-storey model, much of the published articles have a very limited range of application. Quantifying the interaction of different forces in multi-story non-proportional buildings has been the main challenge of these studies. The proposed “shear and bending combination method” solves this by introducing parameters that can determine the relative influence of individual actions. Moreover, the proposed method applies to buildings with all type of structural systems, having asymmetry, and accidental eccentricity. The method is validated through a parametric study consisting of eighty-one building models and using computer analysis. The proposed method and the research findings of this study are useful in determining the torsional stability of the building, in verifying the results of the computer-based analysis, and in optimizing the structural system in the buildings.

TORSION EFFECTS IN BUILDING SEISMIC PERFORMANCE

The paper considers torsion effects that occur during the building response to seismic action. Computation and parametric analysis are conducted for various values of building eccentricity induced by mass and stiffness variation. Such a model accounts for the actual dynamic effect of accidental eccentricity, usually considered in building design by quasi-static value of the torsion moment. Two types of models are employed to explore dynamic parameters of the building. The models are formed using Wolfram Mathematica software in which the mass and stiffness properties are parametrically related to the basic dynamic characteristics of the building. The commercial software package CSI ETABS ver.17 is used for validation of the model. Seismic performance of the building is evaluated, and the results of the parametric analysis are presented using the shear forces and torsion moment. The analysis showed that the nature of eccentricity has a major influence on distribution of seismic forces due to the torsion.

Effects of the Accidental Eccentricity on Regular and Irregular Buildings

The response of any building during seismic loading conditions might be affected by several factors, the horizontal torsion effect which generated by the eccentricity between centre of mass and centre of rigidity has conspicuous impact on the total response of building however, in many of the modern codes this influence is introduced by adopting the accidental eccentricity (AE) concept. In this paper analytical evaluation was done to assess the impact of the accidental torsion on high-rise structures with asymmetrical and symmetrical plan configurations in order to estimate the horizontal torsion effects for both regular and irregular structures during a high-intensity earthquake. The linear-static method, linear-dynamic (RS) method and time history method are the followed procedures for analysing the models, whilst the provisions of the considered codes are the Indian standard provisions and uniform building code 97 provisions, three different conditions were applied the first applying the seismic later load without accidentaleccentricity (AE), the second case is assuming %5 of (AE) which is worldwide presupposed value in many of seismic codes, where the third condition is adapting an accidental-eccentricity (AE) calculated according to the selected seismic codes. ETABS 2016 Software was utilized for analysing all models.

Seismic Design of Box-Type Unreinforced Masonry Buildings Through Direct Displacement-Based Approach

In the last decade, displacement-based seismic design procedures have been recognised to be effective alternatives to force-based design (FBD) methods. Indeed, displacement based design (DBD) may allow the structural engineer to get more realistic predictions of local and global deformations of the structure, and hence damage, under design earthquakes. This facilitates the achievement of performance objectives and loss mitigation in the lifetime of the structure. Nonetheless, DBD needs further investigation for some structural types such as masonry buildings. In this paper, a direct displacement based design (DDBD) procedure for unreinforced masonry (URM) buildings is presented and critically compared to FBD. The procedure is proposed for box-type URM buildings with reinforced concrete slabs, bond beams and lintels above openings, which have shown acceptable seismic performance in severe earthquakes preventing out-of-plane failure modes. Seismic design of a three storey brick masonry building in a high seismicity region is discussed as a case study. The effects of ordinary and near-field design earthquakes, as well as load combinations and accidental eccentricity prescribed by current codes, were investigated. Finally, design solutions provided by FBD and DDBD were optimised and their construction costs were estimated. It was found that, particularly at small epicentral distances, neglecting the combination of horizontal seismic actions and accidental eccentricity may induce significant underestimation and an ideally more uniform distribution of strength demands on URM walls. In addition, construction costs resulting from DDBD may be significantly lower than those related to code based FBD procedures.

Experimental Study on Reinforced Concrete Column Incased in Prefabricated Permanent Thin-Walled Steel Form

Conventional construction methods of reinforced concrete (RC) structures generally require a long construction period and high costs due to many on-site temporary form works. In this study, a prefabricated permanent thin-walled steel form integrated with reinforcement cage (PPSFRC) was developed, and it makes for a fast-built construction by reducing the temporary form works. Axial compression tests were conducted on a total of 9 test specimens to investigate the structural performances of the newly developed columns. The proposed column construction method utilized relatively thinner steel plates compared to conventional concrete-filled tube (CFT) columns, but it was designed to have sufficient resistance performances against the lateral pressure of fresh concrete and to prevent the buckling of the thin plates by utilizing the steel angles and channel stiffeners prefabricated in the permanent thin-walled steel form. The experimental results showed that the column specimens fabricated by the PPSFRC method had better local buckling resistance and behaved in a more ductile manner compared to the conventional CFT columns. In addition, the axial strengths of the test specimens were compared with those estimated by design provisions, and the flexural moments induced by initial imperfection or accidental eccentricity of axial loads were also discussed in detail.

The Effect of Seismic Design Methods on Design Eccentricities in Building with Planar Irregularities

Seismic provisions have utilized design eccentricities to reduce planar irregularities in lateral stiffness of buildings. In calculating a design eccentricity, the dynamic amplification factor may be applied either to accidental eccentricity or to both inherent and accidental eccentricities according to design codes. In this paper, different code provisions and their impact on torsional responses of buildings are investigated using example buildings with various aspect ratios and eccentricities. It was found that dynamic amplification is underestimated if the inherent eccentricity is small, when buildings are designed by seismic provisions using dynamic amplification factors for both to inherent and accidental eccentricities. On the other hand, the design eccentricity determined by applying the dynamic amplification factor only to accidental eccentricity reflects torsional amplification accurately.