Concluding Remarks

Displacement based procedures can directly lead the designer to the key design parameters such as interstory drifts and displacements. If the ductility is distributed according to the ductile design of braces over the height for example based on the elastic modal vibration of the structure, the brace characteristics will interfere with the lateral displacement. The results obtained from these studies have been summarized as follows,

• The modal ductility demand distribution and the resulted force distributions give acceptable results for tall buildings compared to the dynamic analyses. However in order to avoid high strain demand in members in the structural design of the braced buildings, the participation of higher modes must be limited. This issue is generally considered in the capacity design of the structure so that the mass portion of the first mode does not decrease to values less than 70 percents or alternatively reduce the number of modes that own the 98 percents of the system mass.

• As expected the ductility demand in eccentric systems had the highest values having other specifications constant. This ductility was highly dependent to the plastic rotations in the mid length link beams. It has also been shown that the lateral story force has not been so sensitive to the ductility pattern but the displacement and drift directly change with the ductility. The effective damping, total base shear, mass and effective height ratio which may be assumed as the representative for lateral force distribution are not sensitive to the ductility distribution over height and just depend on the maximum ductility value.

• As the relationship between member strains or member plastic rotations with the inter-story drifts are determined, both local and global performance criteria may be used for such a design method.

As shown by various examples, various effects such as column deformation effects, torsional effects, higher mode effects, P — A effects and low cycle fatigue effects may easily be assessed by the use of equivalent procedures in the direct DBD.

Acknowledgment

The supports by the Moshanir Power Engineering Consultant Company are gratefully acknowledged.