T. B. Panagiotakos

DEFORMATIONS OF REINFORCED CONCRETE MEMBERS AT YIELDING AND ULTIMATE

The inelastic deformation capacity of reinforced concrete (RC) members is important for the resistance of RC structures to imposed deformations, and especially so for seismic loads as earthquake-resistant design relies on the ability of RC members to develop (cyclic) deformations well beyond elastic limits without significant loss of load-carrying capacity. This study develops expressions for the ultimate deformation capacity and for the deformation at yielding of RC members in terms of their geometric and mechanical characteristics. Such expressions are essential for the application of displacement-based procedures for earthquake-resistant design of new RC structures and for seismic evaluation of old ones. They are also essential for a realistic estimation of the effective elastic stiffness of cracked RC members and structures, which is important for the calculation of seismic force and deformation demands.

Seismic response and design of RC structures with plan-eccentric masonry infills

The bidirectional response of a two-storey RC frame structure with two adjacent sides infilled is studied through shaking table tests and non-linear dynamic analyses. The pre-cracking stiffness of the infills is large enough to impose twisting of the infilled structure about the common corner of the two infilled sides, with predominant period close to that of translation of the symmetric bare structure in the two horizontal directions. Parametric analyses and test results show that the peak displacement components of the corner column of the two open sides are about the same as (or slightly less than) those of the bare structure under the same bidirectional excitation, but take place simultaneously. This simultaneity of peak local demands from the two components of the motion seems to be the only effect of plan-eccentric infilling that needs to be taken into account in the design of the RC structure. Despite their very high slenderness (height-to-thickness ratio of about 30), infill panels survive out-of-plane peak accelerations of 0.6g at the base of the structure or 1.3-1.75g at their centre.

Estimation of inelastic deformation demands in multistorey RC frame buildings

Estimation of peak inelastic deformation demands is a key component of any displacement-based procedure for earthquake-resistant design of new structures or for seismic evaluation of existing structures. On the basis of the results of over a thousand non-linear dynamic analyses, rules are developed for the estimation of mean and upper-characteristic peak inelastic interstorey drifts and member chord rotations in multistorey RC frame buildings, either bare or infilled in all storeys but the first. For bare frame structures, mean inelastic deformation demands can be estimated from a linear, equivalent static, or preferably multimodal response spectrum analysis with 5 per cent damping and with the RC members considered with their secant stiffness at yielding. 95 per cent characteristic values can be estimated as multiples of the mean deformations. For open-first-storey buildings, the linear analysis can be equivalent static, with the infills modelled as rigid bidiagonal struts and all RC members considered with their secant stiffness to yielding. Copyright

DEFORMATION-CONTROLLED EARTHQUAKE-RESISTANT DESIGN OF RC BUILDINGS

A procedure for deformation-controlled, or displacement-based, seismic design of multistorey RC buildings is proposed, implemented and applied for the full design of a four-storey RC structure. It is integrated into the overall structural design, along with the design for the non-seismic actions and consists of a ULS verification against the conventional strain limits for a frequent “serviceability” earthquake and of proportioning the compression reinforcement and the transverse reinforcement of critical regions of members to meet the member peak inelastic chord rotation demands under the “life-safety” seismic action. Quantitative rules and expressions are proposed for the estimation of (a) mean and upper-characteristic peak inelastic chord rotation demands, through appropriate linear-elastic analyses, and (b) mean and lower-characteristic values of member ultimate chord rotations, in terms of member geometric and material data.

MODELLING OF RC MEMBERS UNDER CYCLIC BIAXIAL FLEXURE AND AXIAL FORCE

A model is proposed for the incremental force-deformation behaviour of reinforced concrete sections and members, under generalised load or deformation histories in 3D, including cyclic loading, up to ultimate deformation. At the section level the model is of the Bounding Surface type and accounts for the coupling between the two directions of bending and between them and the axial direction. For the construction of the member tangent flexibility matrix on the basis of the section tangent flexibility matrix, a piecewise-linear variation along the member is assumed for the nine terms of the tangent section flexibility matrix. Model parameters are derived on the basis of available test results for: (a) the force-deformation response under cyclic biaxial bending with normal force; (b) the hysteretic energy dissipation; (c) the secant-to-yield member stiffness, and (d) the ultimate deformation of the member under cyclic biaxial load paths.

EFFECT OF COLUMN CAPACITY DESIGN ON EARTHQUAKE RESPONSE OF REINFORCED CONCRETE BUILDINGS

In earthquake resistant design of RC frame buildings, capacity design of columns in flexure is applied to eliminate the possibility of storey sway mechanisms and to spread the inelastic deformation...

SEISMIC ASSESSMENT OF EXISTING RC BUILDINGS

Two procedures are presented for seismic assessment of individual RC buildings on the basis of member seismic chord rotation demands. In the (simpler) “preliminary” evaluation procedure, inelastic chord rotation demands are estimated from linear analysis, while forces for brittle failure modes are computed in a capacity-design fashion. In the “final” or “detailed” evaluation, inelastic chord rotation demands and member shears are determined via nonlinear static (pushover) analysis. This procedure also requires more information on as-built materials and reinforcement. Verification criteria at three performance levels are proposed, tuned to be on the conservative side for “preliminary” evaluation.