The Hemilabile Arene:Z Ligand

Based on the results and discussions presented in this thesis, several conclusions are presented in this chapter.

For outrigger-braced structure, the outrigger location for the structure that gives the least deflection is the optimum location for the least along-wind acceleration as the building’s acceleration is directly proportional to the deflection. A series of graphs with one to five outriggers is plotted to show the best location in reducing the building deflection.

Generally, for the optimum performance of a structure with n outriggers, the outriggers should be placed at height locations of

) 1 (

1 +

n ,

) 1 (

2 +

n , up to ) 1 (n+

n . The study shows

that the best location of the outriggers is somewhere at equal distance of the height of the structure from the base; again, this must be based on the building’s properties. On the other hand, the outrigger location that gives the least core moment is located as near as

possible to the building’s foundation. However, this is generally undesirable, as it is not efficient in terms of decreasing building deflection and acceleration.

Two types of wind loading are introduced to act as the lateral load on the structure: a uniformly distributed wind load and a triangular wind load. The results show that the outrigger location tends to move up the building’s height with a triangular load distribution in comparison with uniform wind load distribution acting on an outrigger-braced structure. This is mainly due to the difference in characteristics of wind action on a building, such as the base bending moment and the top deflection of the building itself.

Additionally, a parametric study has been carried out to investigate the factors that affect the efficiency of an outrigger-braced structure in terms of top drift and moment reduction.

In the analysis, the height of a structure is investigated and shows no relationship to the efficiency of the outrigger-braced structures. Similarly, the core properties of an outrigger-braced structure are studied and it is concluded that the stronger the core, with an increase in core properties or in concrete strength, there is a decrease in the efficiency of the outrigger structures. This may be due to the fact that the stronger core attracts more forces and moments, causing less forces and moments to be redistributed to the outrigger-braced core-to-column.

The column sizes have a significant effect on the efficiency of an outrigger-braced system. Deflection and moment reduction efficiency are greatly reduced by increasing the column sizes, on the basis that the outriggers are considered stiff. In conjunction with the column sizes, a longer clear distance between columns yields a higher efficiency in the outrigger-braced system. In short, factors such as the lever arm between outrigger-braced columns, and the properties of the outrigger-braced columns and outriggers, play an important role in the efficiency of an outrigger-braced system in a structure.

In terms of peak along-wind and crosswind acceleration, AS1170.2 is adopted to compare with both analyses. AS1170.2 shows relatively higher peak along-wind acceleration than that which is manually calculated. This is mainly due to the different approach adopted in

AS1170.2 in terms of estimating the top deflection of the structure, which is conservatively modified by adopting the maximum point load that is acting on the tip of the cantilever, and the point load is converted from the total core base moment divided by the total height. In addition, the equation provided by AS1170.2 does not include the mode shape correction factor. Although the equation is transformed into the generalized mass with an assumption of k =1, no additional correction factor, K , is included to _m modify the generalized mass.

For peak crosswind acceleration, both ETABS and manual analyses show relatively higher acceleration, almost double that of the peak crosswind acceleration in AS 1170.2.

This is primarily due to two main factors: one is the higher value of the frequency-dependent crosswind force spectrum, C_Fs, adopted in both the ETABS and manual analysis. The crosswind force spectrum, C_Fs, is a very important factor in determining the crosswind acceleration of the structure and it depends on the building’s natural frequency. However, there is limited information about C_Fs provided in AS1170.2, and most is in terms of the parameters that can be obtained from wind tunnel testing, which might cause problems during the preliminary building design. The second factor is the lower mode shape correction factor specified in AS1170.2. In general, the mode shape correction factor in AS1170.2 is comparatively lower than the correction factor from the proper derivation.

An example of an outrigger-braced structure is analyzed using both ETABS and manual calculation. A comparison between the ETABS analysis and manual calculation shows close results in terms of the restraining moments at the outrigger location, the building frequencies, and the total deflection at the top of the building. However, the results obtained from ETABS are more accurate as it involves detailed 3D analysis, including secondary effects on the structure.

However for tall building design, it is suggested that both approaches are adopted in two different stages. For the preliminary stage, it is advised that an estimation of the

outrigger-braced system through manual calculation is carried out, as opposed to using time-consuming modeling. For the detailed design phase, computer software such as ETABS should be adopted to increase the accuracy of the results.