Asian journal of civil engineering
Volume:10 Issue: 1, Feb 2009

The coupling between form and forces, their structural morphology, is a key point fortensegrity systems. In the first part of this paper we describe the design process of thesimplest tensegrity system which was achieved by Kenneth Snelson. Some other simplecells are presented and tensypolyhedra are defined as tensegrity systems which meetpolyhedra geometry in a stable equilibrium state. A numerical model giving access to morecomplex systems, in terms of number of components and geometrical properties, is thenevoked. The third part is devoted to linear assemblies of annular cells which can be folded.Some experimental models of the tensegrity ring which is the basic component of this“hollow rope” have been realized and are examined.

Tuned mechanical dampers, TMD, are common practical passive devices to increase theeffective structural damping. The sealed, tuned liquid column gas damper, TLCGD, became the cost-effective absorber of similar efficiency. Multi-purpose buildings and towers exhibit moderate or pronounced asymmetry even for a regular geometrical plan. Consequently, the floors are both, obliquely displaced and rotated about the vertical axis during earthquake or wind induced vibrations. The coupled, modal displacement and small rotation combine kinematically to a rotation about the floor’s modal center of velocity. If such a center falls outside of the floor (moderate asymmetry), the ideal position of the mid-plane of the U- or Vshaped TLCGD requires its normal distance from this center maximum. Pronounced asymmetry renders several modal centers within the floor plan: the novel (sealed, torsional) TTLCGD with its in plane curved piping section encloses the center for best efficiency. The uppermost floor is suitable to host all those modally tuned absorbers. For higher modes, a floor at intermediate height might become suitable. Tuning, in a first step becomes easy by means of the elaborated geometric analogy to the equivalent TMD or (torsional) TTMD. Subsequently performed finetuning of frequency and damping in state-space renders an even more robust control, especially if smaller absorber units in parallel action are applied. The optimal absorber frequency is adjusted by assigning the equilibrium gas pressure, the novel control parameter resulting from the sealed design. Optimal damping of the fluid flow may require an orifice plate built in the piping system. Numerical simulations illustrate the effectiveness of these liquid absorbers to mitigate the earthquake or wind induced vibrations of plan-asymmetric buildings.

Passive, active and hybrid vibration control of structures during earthquakes were studied.Particular attention was given to hybrid preview control strategy for protection of structures against earthquakes. A three-story building under fixed-base condition and with laminated rubber bearing base isolation system subject to the El Centro 1940 earthquake were analyzed. The cases that an active control system with and without preview was present were studied in details. The corresponding structural responses with passive, active and hybrid vibration control systems were evaluated. Accelerations and displacements responses for active systems with and without preview sensors for fixed-base and base-isolated structures were computed and the results were compared with those for the unprotected building. It was shown that properly designed passive, active and hybrid control systems could effectively reduce the acceleration transmitted to structures during a major earthquake.It was also shown that the inclusion of the preview sensors in the active control strategyimproved the system performance considerably. The hybrid use of the laminated rubberbearing isolation system with the active control strategies could provide significantimprovement of the protection of buildings during seismic events.

This paper explores the effects of adding steel fibres to high-strength reinforced concretecolumns and in particular only to the cover of the columns. An experimental program wasconducted where seven circular reinforced concrete columns were tested with varying fibre content – one contained no fibres, three contained fibres throughout the cross-section and three contained fibres only in the outer concrete. The other column properties were kept the same for all the seven columns. All seven columns were tested by the application of a concentric, axial compression force. It was found that although only minor improvements were noticeable for a fibre content of 1%, the addition of 1.5% and 2% steel fibres increased the load at which cover spalling took place. It was also found that the columns containing both FHSC (fibrous high strength concrete) in the outer concrete and HSC in the core exhibited higher levels of ductility than the columns containing FHSC throughout the entire cross-section.

Domes supply unimpeded wide spaces and they encompass a maximum amount of areaswith a minimum surface. They are also exceptionally suitable structures for covering placeswhere minimum interference from internal supports are required. The behavior of latticeddomes is nonlinear due to change of geometry under external loads. This is due to theimperfections arising either from the manufacturing process and/or from the construction of the structure. In this paper, the optimum topological design problem of geometricallynonlinear single layer network dome is considered. The design problem is formulated suchthat the total number of rings, the height of the crown, and the steel pipe section designations required for the member groups in the dome are treated as design variables. The design limitations that consist of serviceability and strength constraints are implemented from LRFD-AISC. The solution of this discrete programming problem is determined by using the harmony search algorithm. This algorithm simulates jazz improvisation into a numerical optimization technique. Design example considered shows the effectiveness and robustness of the algorithm developed.

An efficient algorithm is presented for the formation of statical basis, corresponding tohighly sparse flexibility matrices for structures. This is achieved by applying a modified antcolony optimization algorithm for the formation of localized self-equilibrating systems. Theefficiency of the present algorithm is illustrated through simple truss examples