twenty seven masonry construction: www.theeagle.com beams & - PowerPoint PPT Presentation

E LEMENTS OF A RCHITECTURAL S TRUCTURES : F ORM, B EHAVIOR, AND D ESIGN ARCH 614 D R. A NNE N ICHOLS S PRING 2018 lecture twenty seven masonry construction: www.theeagle.com beams & columns Masonry Construction 1 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Design • Masonry Standards Joint Committee – ACI, ASCE, TMS – ASD (+empirical) • linear-elastic stresses – LRFD added in 2002 – referenced by IBC – unreinforced allows tension in flexure – reinforced - all tension in steel – walls are also in compression International Masonry Institute (Brian Trimble) Masonry Construction 2 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Beam & Wall Design • reinforcement increases capacity & ductility Masonry Construction 3 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Design • f s is not the yield stress • f m is the stress in the masonry STRAIN STRESS  m f m C m =f m b(kd)/2 kd d n.a. jd M t  s f s /n T s =A s f s A s grout unit A s   bd BIA Teknote 17 series Masonry Construction 4 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Materials • units – stone, brick, concrete block, clay tile Masonry Construction 5 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Materials • mortar – water, masonry cement, sand, lime – types: • M higher strength – 2500 psi (ave.) A • S medium high strength – 1800 psi O • N medium strength – 750 psi W • O medium low strength – 350 psi R • K low strength – 75 psi Masonry Construction 6 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Materials • rebar • grout – fills voids and fixes rebar • prisms – used to test strength, f  m • fire resistant Masonry Construction 7 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

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 8 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Allowable Masonry Stresses • tension - unreinforced only Masonry Construction 9 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Walls tension normal to bed joints Not allowed in MSJC codes tension parallel to bed joints weak units strong units Masonry Construction 10 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Allowable Masonry Stresses • flexure – F b = 1/3 f’ m (unreinforced) – F b = 0.45 f’ m (reinforced) • shear, unreinforced masonry   120 psi – F v = 1 . 5 f m • shear, reinforced masonry – M/Vd  0.25: F v =  3 0 . f m  – M/Vd  0.25: F v = 2 . 0 f m Masonry Construction 11 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

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 12 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Reinforcement, M s C m =f m b(kd)/2 kd d n.a. jd t T s =A s f s A s grout kd   F=0: A f f b unit s s m 2   ρbd 2 M A f jd jf  M about C m : s s s 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 13 Architectural Structures III S2018abn Lecture 23 ARCH 631

Reinforcement, M m C m =f m b(kd)/2 kd d n.a. jd t T s =A s f s A s grout unit for equilibrium: kd   0   2 M M f b jd 0 . 5 f bd jk about F s m m m 2 if f m =F b (allowable) the moment capacity is limited by the masonry MSJC F b =0.33f’ m Masonry Construction 14 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Lintels • distributed load – triangular or trapezoidal Masonry Construction 15 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

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 M  • 2 needs to be sized bd  jF for shear also s • get b & d in nice units M s  – size reinforcement (bar size & #): A F jd   – check design: s M A F jd M s s s M   f F b b 2 0 . 5 bd jk Masonry Construction 16 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Ultimate Strength Design • LRFD • like reinforced concrete • useful when beam shear is high • improved inelastic  0.80 f’ m c 1 model 2 C – ex. earthquake loads  1 c T Masonry Construction 17 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Columns and Pilasters • must be reinforced Masonry Construction 18 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Columns and Pilasters • considered a column when b/t<3 and h/t>4 • b is width of “wall” • t is thickness of “wall” • slender is – 8” one side – h/t  25 • needs ties • eccentricity may be required Masonry Construction 19 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Columns – allowable axial load   2     h         0 25 0 65 1 P . f A . A F a m n st s     140 r   h/r  99 2     70 r      P 0 . 25 f A 0 . 65 A F a m n st s   h h/r > 99 h = effective length A n = effective area of masonry A st = effective area of column reinforcement F s = allowable compressive stress in column reinforcement (lesser of 0.4f y or 24 ksi) Masonry Construction 20 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Masonry Walls (unreinforced) – allowable axial stresses   2 2     70 r h            F 0 . 25 f F 0 . 25 f 1 a m a m       h 140 r   h/r  99 h/r > 99 Masonry Construction 21 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Design • masonry columns and walls (unreinforced) f f     a b f f F 1 . 0 and b a t F F a b   2   h        – h/r < 99 F 0 . 25 f 1 a m     140 r   2   70 r     – h/r > 99 F 0 . 25 f a m   h   F 0 . 33 f b m Masonry Construction 22 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Design • masonry columns and walls - loading – wind loading P e w – eccentric axial load – “virtual” eccentricity, e 1 h P P e o e o w w M e  1 P V V M e 1 virtual eccentricity P P Masonry Construction 23 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Design • masonry columns and walls – with rebar – wall reinforcement usually at center and ineffective in compression   f  f f F F provided a b b a a BENDING STRESS AXIAL STRESS f m C m =f m b(kd)/2 f a = P/A d n.a. jd M t f s /n T s =A s f s A s grout unit     F P C T for equilibrium: m s Masonry Construction 24 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614

Design Steps Knowing Loads 1. assume limiting stress • buckling, axial stress, combined stress 2. solve for r, A or S 3. pick trial section 4. analyze stresses 5. section ok? 6. stop when section is ok Masonry Construction 25 Elements of Architectural Structures S2018abn Lecture 27 ARCH 614