Keywords: rehabilitation, strengthening, base plate, steel structure, rehabilitation of base plates, strengthening of base plates.

In structural retrofitting, a variety of parameters such as changes in the loading values, structural system, loading patterns, transmittal paths of structural loads, etc. [1,2] especially, with inefficiencies in the preliminary design, can change loading condition and, or increase the loading values on the base plates. In some cases this problem can cause uplift in the columns. In these situations the state of the base plate will be changed. Obviously, in all of these conditions, especially in latter condition, the base plate under new conditions should be studied carefully to find an appropriate solution.

In a research project with the aim of retrofitting of 12,000m² of complicated steel structures [3], several structural members, such as the columns, beams and bracings had to be significantly retrofitted. The inefficiencies resulted from changes in building codes, mistakes in modeling, loading inaccuracies, inadequate construction procedures, poor supervision, etc. In spite of the lightening of the floors, decreasing the loads and maintaining better load distribution, many columns and bracings still required large amounts of strengthening, including for example an increased cross section. Uplift also occurred for some columns. Therefore it was necessary to study, redesign and strengthen the aforementioned base plates under these conditions to modify their behaviour. Structural analysis and design was carried out using the SAP [4] software and the FOUND [5] and SAFE [6] software was used for the foundation analysis and design.

In this project some inventive methods were proposed and applied to address these deficiencies. Also in some cases, extension of the dimension and an increase of the stiffness of the base plate was used as a favourite and relatively inexpensive method for avoiding difficulties with foundations, especially punching shear. These methods were comparatively inexpensive and achieved good results. In general, the proposed methods proved to be economically viable.

1

FEMA-356, "Pre-standard and Commentary for Rehabilitation of Building", Washington DC, Federal Emergency Management Agency, 2000.

2

Manual of Seismic Rehabilitation of Existing Buildings, International Institute of Earthquake Engineering and Seismology, Iran, 2009.

3

M. Foroughi, "Study of retrofitting procedures of art and cultural center of Yazd University", University of Yazd, Iran, 2010.

4

SAP2000 advanced 12.0.0, "Structural analysis program", Computers and Structures, Inc., University Ave., Berkeley CA, USA, 1995.

5

FOUND, "Analysis and Design of Square and Rectangular Footing", Seyed Jalaladdin Tabatabeee, Mir Afshin Niakooee, 1995.

6

SAFE Plus W/Detailer Version 8.1.1, "Slab Analysis by the Finite Element Method", CComputers and Structures, Inc., University Ave., Berkeley CA, USA, 1995.

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