| Summary: | Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. === ENGLISH ABSTRACT: Reinforced concrete structures, designed according to proper capacity design guidelines, can deform
inelastically without loss of strength. Therefore, such structures need not be designed for full elastic
seismic demand, but could be designed for a reduced demand. In codified design procedures this
reduced demand is obtained by dividing the full elastic seismic demand by a code-defined behaviour
factor. There is however not any consensus in the international community regarding the appropriate
value to be assigned to the behaviour factor. This is evident in the wide range of behaviour factor
values specified by international design codes.
The purpose of this study is to assess the seismic drift of reinforced concrete structural walls in order
to evaluate the current value of the behaviour factor prescribed by SANS 10160-4 (2009). This is
done by comparing displacement demand to displacement capacity for a series of structural walls.
Displacement demand is calculated according to equivalency principles (equal displacement principle
and equal energy principle) and verified by means of a series of inelastic time history analyses (ITHA).
In the application of the equivalency rules the fundamental periods of the structural walls were based
on cracked sectional stiffness from moment-curvature analyses.
Displacement capacity is defined by seismic design codes in terms of inter storey drift limits, with the
purpose of preventing non-structural damage in building structures. In this study both the
displacement demand and displacement capacity were converted to ductility to enable comparison.
The first step in seismic force-based design is the estimation of the fundamental period of the
structure. The influence of this first crucial step is investigated in this study by considering two period
estimation methods. Firstly, the fundamental period may be calculated from an equation provided by
the design code which depends on the height of the building. This equation is known to overestimate
acceleration demand, and underestimate displacement demand. The second period estimation
method involves an iterative procedure where the stiffness of the structure is based on the cracked
sectional stiffness obtained from moment-curvature analysis. This method provides a more realistic
estimate of the fundamental period of structures, but due to its iterative nature it is not often applied in
design practice.
It was found that, regardless of the design method, the current behaviour factor value prescribed in
SANS 10160-4 (2010) is adequate to ensure that inter storey drift of structural walls would not exceed
code-defined drift limits. Negligible difference between the equivalency principles and ITHA was
observed. === AFRIKAANSE OPSOMMING: Gewapende beton strukture wat ontwerp is volgens goeie kapasiteitsontwerp-riglyne kan plasties
vervorm sonder verlies aan sterkte. Gevolglik hoef hierdie strukture nie vir die volle elastiese
seismiese aanvraag ontwerp te word nie, maar kan vir 'n verminderde aanvraag ontwerp word. In
gekodifiseerde ontwerpriglyne word so 'n verminderde aanvraag verkry deur die volle elastiese
aanvraag te deel deur 'n kode-gedefinieerde gedragsfaktor. Wat egter duidelik blyk uit die wye reeks
van gedragsfaktor waardes in internasionale ontwerp kodes, is dat daar geen konsensus bestaan in
die internasionale gemeenskap met betrekking tot die geskikte waarde van die gedragsfaktor nie.
Die doel van hierdie studie is om seismiese verplasing van gewapende beton skuifmure te evalueer
ten einde die waarde van die gedragsfaktor wat tans deur SANS 10160-4 (2009) voorgeskryf word te
assesseer. Dit word gedoen deur verplasingsaanvraag te vergelyk met verplasingskapasiteit.
In hierdie studie word verplasingsaanvraag bereken deur middel van gelykheidsbeginsels (gelyke
verplasingsbeginsel en gelyke energiebeginsel) en bevestig deur middel van nie-elastiese
tydsgeskiedenis analises (NTGA). Die effek van versagting as gevolg van nie-elastiese gedrag word
in aanmerking geneem in die toepassing van die gelykheidsbeginsels.
Verplasingskapasiteit word deur seismiese ontwerpkodes gedefinieer deur perke te stel op die
relatiewe laterale beweging tussen verdiepings, met die doel om nie-strukturele skade te verhoed.
Om verplasingsaanvraag en -kapasiteit te vergelyk in hierdie studie, word beide omgeskakel na
verplasingsduktiliteit.
Die eerste stap in kraggebaseerde seismiese ontwerp is om die fundamentele periode te beraam. Die
invloed van hierdie eerste kritiese stap word in hierdie studie aangespreek deur twee
periodeberamingsmetodes te ondersoek. Eerstens kan die fundamentele periode bereken word deur
'n vergelyking wat 'n funksie is van die hoogte van die gebou. Dit is egter algemeen bekend dat
hierdie vergelyking versnellingsaanvraag oorskat en verplasingsaanvraag onderskat. Die tweede
metode behels 'n iteratiewe prosedure waar die styfheid van die struktuur gebaseer word op die
gekraakte snit eienskappe, verkry vanaf 'n moment-krommingsanalise. 'n Beter beraming van die
fundamentele periode word verkry deur hierdie metode, maar as gevolg van die iteratiewe aard van
die metode word dit selde toegepas in ontwerppraktyk.
Die resultate van hierdie studie toon dat die huidige waarde van die gedragfaktor soos voorgeskryf in
SANS 10160-4 (2010) geskik is om te verseker dat die relatiewe laterale beweging tussen verdiepings
binne kode-gedefinieerde perke sal bly. Onbeduidende verskil is waargeneem tussen die resultate
van gelykheidsbeginsels en NTGA.
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