APPLIED ARCHITECTURAL STRUCTURES: STRUCTURAL ANALYSIS AND SYSTEMS DR. ANNE NICHOLS FALL 2018 lecture twenty three masonry construction Bright Football Complex www.tamu.edu Masonry Construction 1
Learning Evaluation Masonry Construction 2
www.archiplanet.org Masonry columns beams arches walls footings Masonry Construction 3 http://www.bluffton.edu
Masonry Construction solid, grouted, hollow unreinforced reinforced prestressing Masonry Construction 4
Masonry Materials brick concrete masonry units Masonry Construction 5
Masonry Materials mortar water, masonry cement, sand, lime types: M A S O N W O R K higher strength 2500 psi (ave.) medium high strength 1800 psi medium strength 750 psi medium low strength 350 psi low strength 75 psi Masonry Construction 6
Masonry Materials reinforcement deformed bars prestressing strand development length anchorage splices ties steel or composite Masonry Construction 7
Masonry Materials grout high slump concrete fills voids and fixes rebar prisms used to test strength, f m unit t b t m mortar Masonry Construction 8 mortar > unit
Masonry Materials fire resistance fire-resistive structural material details important to prevent leaks or cracks retains strength if exposure not too long mortar and cmu s dehydrate loses 30-60% after that no toxic fumes cover necessary to protect steel Masonry Construction 9
Masonry Materials moisture resistance weathering index for brick bond and detailing expansion or shrinking from water provide control joints parapets, corners, long walls parapet with no control joint Masonry Construction 10
Masonry Walls based on empirical requirements for minimum wall thickness and height h/t < 25 wall thicknesses often increased by 4 /story bearing walls > 3-5 stories uneconomical, steel or concrete frames used strength design limit states: serviceability: deflection ultimate: compression & tension Masonry Construction 11
Masonry Walls compression + bending P h e f a P A axial stress P bending stress M=Pe f b Mc I M S M e P virtual eccentricity combined fa f b P A M S fb f a Masonry Construction 12
Masonry Walls equivalent eccentricity with lateral load P e o w P e o w M P V P e 1 V e 1 M P virtual eccentricity Masonry Construction 13
Masonry Walls tension normal to bed joints Not allowed in MSJC code tension parallel to bed joints strong units weak units Masonry Construction 14
Masonry Beam & Wall Design MSJC (ACI, ASCE, TMS) limit tensile stress in mortar working stress design (ASD) linear stresses in masonry no tension in masonry when reinforced elastic stress in steel < f y additional compression in walls masonry strength = f m Masonry Construction 15
Masonry Beam & Wall Design reinforcement increases capacity & ductility Masonry Construction 16
Masonry Design f s is not the yield stress f m is the stress in the masonry STRAIN STRESS t d grout n.a. A s kd s m f s /n f m T s =A s f s C m =f m b(kd)/2 jd M M unit BIA Teknote 17 series A s bd Masonry Construction 17
Allowable Masonry Stresses tension - unreinforced only Masonry Construction 18
Allowable Masonry Stresses flexure F b = 1/3 f m (unreinforced) F b = 0.45 f m (reinforced) shear, unreinforced masonry F v = 1. 5 f m 120 psi shear, reinforced masonry M/Vd 0.25: F 3.0 f v = m M/Vd 1.0: F v = 2. 0 f m Masonry Construction 19
Allowable Reinforcement Stress tension a) Grade 40 or 50 F s = 20 ksi b) Grade 60 F s = 32 ksi c) Wire joint F s = 30 ksi *no allowed increase by 1/3 for combinations with wind & earthquake did before 2011 MSJC code Masonry Construction 20
Reinforcement, M s C m =f m b(kd)/2 t d n.a. kd grout unit A s T s =A s f s jd M about C m : F=0: M s A s f A s s f s f jd m b kd 2 ρbd 2 jf s if f s =F s (allowable) the moment capacity is limited by the steel MSJC: F s = 20 ksi, 32 ksi or 30 ksi by type Masonry Construction 21
Reinforcement, M m C m =f m b(kd)/2 t d n.a. kd grout unit A s T s =A s f s jd M about T s : M F=0: m f A m b s f s kd 2 jd f m b kd 2 0.5f m bd 2 jk if f s =F s (allowable) the moment capacity is limited by the steel MSJC F b =0.33f m Masonry Construction 22
Masonry Lintels distributed load triangular or trapezoidal Masonry Construction 23
Strategy for RM Flexural Design to size section and find reinforcement find b knowing f m and f y size section for some < b get k, j bd M jf s 2 needs to be sized for shear also get b & d in nice units size reinforcement (bar size & #): check design: M f b As Fs jd M M F 2 0. 5bd jk s b A s M F jd s Masonry Construction 24
Ultimate Strength Design LRFD like reinforced concrete useful when beam shear is high improved inelastic model ex. earthquake loads 1 c 0.80f m 1 c 2 C T Masonry Construction 25
Masonry Walls one-way or two-way bending usually use hollow units (< 75% solid) reinforcement grouted into cells if hollow units between wythes if solid reinforcement usually at center reinforcement in compression ineffective avoid stirrups desirable in seismic zones Masonry Construction 26
Masonry Walls axial force-moment interaction diagram f F a a f F b b 1 Masonry Construction 27
Masonry Shear Walls bearing, bending, and shear compression increases resistance f v VQ I b n unreinforced or reinforced unreinforced stress limit 1.5 f 120 psi V A nv F v m Masonry Construction 28
Masonry Shear Walls (and beams) reinforcement strength included: where 1 M P Fvm 4. 0 1. 75 fm 0. 25 2 Vd An A vfsd Fvs 0. 5 Anvs stress limit depends on ratio of bending moment to overturning moment: M/Vd spacing limits Masonry Construction 29 F v = F vm + F vs
Masonry Shear Walls model as deep cantilever beam flexure reinforcement shear stirrups d Masonry Construction 30
Masonry Columns and Pilasters must be reinforced Masonry Construction 31
Masonry Columns and Pilasters considered a column when b/t<3 and h/t>4 slender is 8 one side h/t 25 needs ties eccentricity 10% of side dimension required interaction diagrams like r/c Masonry Construction 32
Masonry Columns allowable axial load P P a a 0. 25 f m h/r 99 h/r > 99 A n 0. 65 A st F s h 1 140 70 0 25 0 65 r. f m An. AstFs h 2 r 2 h = effective length r = radius of gyration A n = effective area of masonry A st = effective area of column reinforcement F s = allowable compressive stress in column reinforcement Masonry Construction 33
Masonry Pilasters, Arches column in wall increase bearing area and stiffness www.tamu.edu Masonry Construction 34
Construction Supervision proper placement of all reinforcement prism construction masonry mortar hot/cold weather protection Masonry Construction 35