STRUCTURAL PROBLEMS IN THE DESIGN OF LARGE MASONRY HALLS

Transcription

1 1488 STRUCTURAL PROBLEMS IN THE DESIGN OF LARGE MASONRY HALLS PROF. K.-J. SCHNEIDER Fachhchschule Bielefeld I Abteilung Minden ArtilleriestraBe 9, D-4950 Minden, Germany ABSTRACT lhe paper deals with sme structural prblems arlslng with the cnstruc f a cvered market having the dimensins 50 x 20 m and a height f 4,5 Fur structural variatins are analysed. Structural stability, stresses in bending and shear, as well as reinfrced masnry as an alternative structural slutin are utlined. INTRODUCTlON Using a cvered market as an example the structural prblems f large masnry halls are utlined. lhe rf f the hall cnsists f a timber truss with a gradient f 30 0 C (cf. fig 1). Fr aesthetical, physical and technical reasns nly masnry materials are t be used. Fur struc ral variatins in terms f lateral lad resistance are lked at: 1. Hrizntal diaphragm being cnfined by vertical diaphragms at ends. 2. Masnry pilasters at 6,25 m centers. 3. Reinfrced cncrete clumns fixed int single fundatins which are cvered by masnry f 115 mm thickness. 4. Fixed reinfrced masnry clumns. lhe masnry walls are tpped with a r.c. r r.m. ring beam. lhey are calculated as slabs under wind lad restrained by the vertical stif ning elements and the hrizntal supprts (grund flr slab, ring beam abve). Lad is taken biaxially. Depending n the lcal cnditins expans jints at 15 t 25 m centers shuld be prvided. In additin t the stability the fllwing is lked at mre els (a) stresses at gaping cracks fr sectins ther than rectangular (l-se tins, crss-sectins)

2 , ,w. l a Figure 1

3 1490 (b) shear stresses in cmbined sectins (c) r.m. beams and clumms. STRUCTURAL STABILITY Fr large masnry halls the mst severe prblem is the structural stability. In principle, these are tw pssibilities t transfer wind lads t the fundatin: (a) Hrizntal diaphragm n tp f the wall: Out-f-plan wind lads are taken by the wal1s as vertlca1 slmp1e spanned beams and transferned t bttm (bttm slab) and n tp f the diaphragms. Vertical lad frm the rf and the wall shall be sufficient t allw fr a gaping crack width f half f the wall thickness at mst The upper hrizntal diaphragm is supprted n vertical masnry diaphragms which transfer the wind lad int the fundatin. (b) N hrizntal diaphragm n tp f the wall : In this case ut-f-plan wlnd lads cause slab actin f the wa11 and are transferred directly int the stiffening elements (pilasters, fixed clumns), and further t the fundatins. Halls with hrizntal diaphragms at rf level (fig. 2) The rf cnstructin is a timber truss. In the plane f the bttm chrd fur hrizntal truss diaphragms with 25 m in length are prvided parallely t the lngitudinal walls (Ps. 3 in fig 2). Wind lades (perpend t the lngitudinal walls) are transferred t the knts f the hrizntal truss diaphragms thrugh the U-shaped r.c. ring beams (Ps. 2a). The hrizntal truss diaphragms are supprted n tp f the masnry pilasters (Ps. 4 and 6). Wind lads perpend t the gable walls are transferred by a 20 m span ring beam directly t tw vertical wall diaphragms (P s. 5). Fr the stiffening parts f the wall (Ps. 4 t 6) the fllwing was verified: (a) structural stability (safety factr 1,5) (b) safety against failure (vertical lads, wind, deviatin frm the verti cal) (c) shear strength (un it failure, mrtar jint failure, edge strain). Halls withut hrizntal diaphragms at rf level Stiffening by pilasters (fig. 3) : All masnry walls are tpped with a r.m. ring beam (Ps. 10). Each wall segment is tw-way spanned between the hrizntal supprts (ring beam and grund slab) and the vertical supprts (pilasters, Ps 11). In the hrizntal divectin a certain tensile strength fr the masnry was adpted. Vertically, gaping cracks were assumed.

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6 1493 The pilasters (Ps. 11) were calculated i analgy t the previus chapter. The calculatin is relatively cmplicated because in a first step the neutral axis f the circle sectin must be determined iteratively (e.g. accrding t /1/). Then ultimate state design is carried ut fr the edge. Fr the shear design nly the area subjected t cmpressin may be taken int accunt. The ring beam is designed with the well-knwn kh-methd (cf. /4/). The structural design presented herein will nt be f great practical imprtance in this frm because erecting the pilasters will be relatively expensive. Hwever, this variatin f cnstructin might gain sme imprtance in case f a rf with lwer gradient r a flat rf. In this cases the smaller wind lads wuld permit the dimensins f the pilasters t be cnsiderably smaller. Stiffening by reinfrced cncrete clumns (fig. 4): An ecnmical alternatlve t masnry pllasters are flxed r.c. clumns. The clumns are cated by masnry frmwrk units. The frmwrk units are cnnected t the adjacent masnry with structural reinfrcement (fig. 4). Stiffening with reinfrced masnry clumns (fig. 5): The clumns fixed int the fundatln are made f frmwrk unlts havlng cavities fr the vertical reinfrcement (fig. 5). Cmpared t r.c. clumns this structural variatin has advantages in terms f heat cnductivity. The ttal uter area f the hall cnsists f masnry s that there is n thermal bridge. All walls have a unifrm aesthetical pattern. REFERENCES 1. Schweda, E., Baustatik-Festigkeitslehre, Werner-Verlag, Düsseldrf, 2. Auflage Phl, R., Schneider, K.-J. and Wrmuth, R., Mauerwerksbau, Werner Verlag Düsseldrf, 2. Auflage 1987

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8 l t I ayer [!J [!] I LI [!] 1Il!:1 11 II'Z; CD HLz 12/1.2 lace. t OtN - Cde) shaped brieks elumn reinfreement reinfreement f ring beam galvanized... ~ \O Vl nd layer Figure 5