Displacement-based seismic rehabilitation of non-ductile RC frames by olliegoblue32


									Displacement-based seismic rehabilitation of non-ductile RC frames
                     with added shear walls

                                       Haluk Sucuoğlu1 and Can Karageyik


Non-ductile reinforced concrete frame buildings constitute an important part of the seismically
vulnerable buildings on the world. Collapse of non-ductile multi story concrete buildings during
strong earthquakes in the past resulted in severe casualties and economic losses. Their
rehabilitation through retrofitting is a critical issue in reducing seismic risks worldwide.
Sub-standard buildings cannot satisfy the basic safety requirements of modern seismic codes
because of insufficient material strengths, poor detailing and lack of seismic design concept
which eventually lead to brittle response under seismic effects. Retrofitting of non-ductile RC
buildings in the past had been mostly based on adding new reinforced concrete shear walls. New
walls improve base shear capacity of existing frame system as well as increasing lateral rigidity.
Increase in both lateral load capacity and lateral stiffness results in decrease of deformation
demands. Transition from shear frame behavior into shear wall behavior is another feature that
further reduces the demands on existing columns. This is indeed a rational approach because
increasing the deformation capacity of the non-ductile frame system composed of non-ductile
structural members is usually unpractical and uneconomical.
Typical floor plan of a four story building retrofitted with shear walls and perhaps unnecessary
column jacketing is shown in Fig. 1. The capacity curves in Fig. 2 reveals the increase in base
shear capacity which in turn leads to reduced displacement demands presented in the table below
both for IO and LS performance levels. It is crucial to note in Fig. 3 the reduction in the
excessive displacement and interstory drift demands at the lower stories, at the target
displacement demand of the retrofitted building. Moreover inter-story drift ratios approach a
uniform distribution over the height of the retrofitted building.
                                            Target Roof Displacement Demands (m)
             Level                +X (Long) Direction                    +Y (Short) Direction
                         Existing Building Retrofitted Building Existing Building Retrofitted Building
               IO              0.163                0.064                0.101                0.031
               LS              0.244                0.103                0.153                0.061

A displacement based approach is presented in this study for the seismic retrofitting of medium
height non-ductile concrete frames. The deformation capacity of the existing critical columns
control design. A minimum amount of shear walls are added for maintaining the deformation
levels below the critical level dictated by the existing columns, which are usually at the ground
story. Detailing of shear walls are based on conforming to the reduced deformation demands of
the retrofitted frame/wall system. Member end rotations are employed as the parameters for
performance evaluation. Initial results obtained from the proposed displacement based approach
have revealed that jacketing of columns and confining the end regions of added shear walls are
usually unnecessary compared to the conventional force-based approach, where excessive force
and deformation capacities are provided without regarding for the actual deformation demands.
    Department of Civil Engineering, Middle East Technical University, Ankara, Turkey.   sucuoglu@ce.metu.edu.tr
                                                                                                                                   New shear wall added to the existing building
                                                                                                                                   RC jacketed column
                                                                                                                                   FRP jacketed column

                                                                                                                              Figure 1

                                                                                                                            Capacity Curves

                                              Base Shear (kN)

                                                                                                                                                                            Existing Building (Long Direction)

                                                                15000                                                                                                       Retrofitted Building (Long Direction)
                                                                                                                                                                            Existing Building (Short Direction)
                                                                                                                                                                            Retrofitted Building (Short Direction)


                                                                         0              0.05          0.1            0.15           0.2               0.25           0.3           0.35          0.4          0.45

                                                                                                                            Roof Displacement (m)

                                                                                                                              Figure 2

                                       Story Displacement Profiles                                                                                                                        Inter-story Drift Ratios
        4                                                                    0.0610                               0.1030                          4
                                                                                                                                                                                                                     Existing Building (Long Direction)
                                                                                                                                                                                                                     Retrofitted Building (Long Direction)
                                                                                                                                                                                                                     Existing Building (Short Direction)
        3                              0.0453                      0.0540                0.0750             0.0965                                3                                                                  Retrofitted Building (Short Direction)

        2                 0.0294   0.0424                   0.0474                                0.0846                                          2

        1       0.0140        0.0239                            0.0484                Existing Building (Long Direction)                          1
                                                                                      Retrofitted Building (Long Direction)
                                                                                      Existing Building (Short Direction)
                                                                                      Retrofitted Building (Short Direction)
        0                                                                                                                                         0
            0            0.02          0.04                         0.06                 0.08               0.1             0.12                      0      0.002         0.004     0.006      0.008      0.01       0.012      0.014     0.016      0.018
                                          Story Displacement (m)                                                                                                                            Inter-story Drift Ratio

                                                                                                                              Figure 3

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