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Masonry Structures, Lectures 2-3, slide 1 Classnotes for ROSE School Course in: Masonry Structures Notes Prepared by: Daniel P. Abrams Willett Professor of Civil Engineering University of Illinois at Urbana-Champaign October 7, 2004 Lesson 2 and 3: Properties of Masonry Materials Introduction, compressive strength, modulus of elasticity condition assessment, movements Masonry Structures, Lectures 2-3, slide 2 Historical Use of Masonry as a Structural Material

Lecture 2 3 Compression, Condition Assess

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Dan Abrams + Magenes Course on Masonry

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  • Classnotes for ROSE School Course in: Classnotes for ROSE School Course in: Masonry Structures Masonry Structures Lesson 2 and 3: Properties of Masonry Materials Introduction, compressive strength, modulus of elasticity condition assessment, movements Notes Prepared by: Daniel P. Abrams Willett Professor of Civil Engineering University of Illinois at Urbana-Champaign October 7, 2004 Masonry Structures, Lectures 2-3, slide 1 Historical Use of Masonry as a Structural Material Masonry Structures, Lectures 2-3, slide 2
  • The First Building Material The first masonry structures were constructed of mud, sun- dried brick. The people of Jericho were building with brick more than 9000 years ago. Sumerian and Babylonian builders covered brick walls with kiln-baked glazed brick. Mesopotamian builders Etemenanki Ziggurat constructed temple towers from height 91 meters 4000 BC to 600 BC. Masonry Structures, Lectures 2-3, slide 3 The First Building Material Stone masonry was used for Egyptian pyramids c. 2500 BC. Pyramid of Khufu at Giza measured 147 m. high and 230 m. square. Pyramid of Khafre at Giza was constructed without cranes, pulleys or lifting tackle. No mortar or adhesive was used. Ancient examples of Cyclopean masonry found throughout Pyramid of Khafre at Giza Europe, China and Peru. Egyptian houses made of mud- brick walls. Masonry Structures, Lectures 2-3, slide 4
  • Greek and Roman Architecture Early Greek architecture (3000 to 700 BC) used massive stone blocks for walls, and early vaults and domes. Greeks constructed with limestone and marble. Romans constructed with concrete, terra cotta and El Puente Aqueduct fired clay bricks. near Segovia Spain Romans refined arch, vault 1st Century AD and dome construction to two tiers of arches 28. 5m tall construct great aqueducts, coliseums and palaces were built with clay brick. Masonry Structures, Lectures 2-3, slide 5 Applications in China The Great Wall of China was constructed from 221 to 204 BC. The wall winds 2400 km from Gansu to the Yellow Sea, and is the longest human-made structure in the world. The wall is constructed of Great Wall of China earth and stone with a brick 6 to 15m. tall facing in the eastern part. 4.6 to 9.1m wide at base ave. 3.7 m wide at top Masonry Structures, Lectures 2-3, slide 6
  • Byzantine Architecture Huge domed churches were built on a scale far larger than achieved with the Romans. Innovative Byzantine technology allowed architects to design a basilica with an immense dome over an open, square space. Isalmic architects developed a rich variety of Hagia Sophia, Istanbul pointed, scalloped, constructed 532-537 AD horseshoe and S-curved dome fell after earthquake in 563 arches for mosques and palaces. Masonry Structures, Lectures 2-3, slide 7 Masonry in the Americas Early pyramids built c. 1200 BC at the Olmec site of LaVenta in Tabasco Mexico. Later monuments constructed by the Maya, Toltecs and Aztecs in central Mexico, the Yucatan, Guatemala, Honduras, El Salvador and Peru were based on the Olmec plan. Four-sided, flat-topped Pyramid of the Sun polyhedrons with stepped Teotihuacan Mexico sides. 66-m. high 2nd century AD Masonry Structures, Lectures 2-3, slide 8
  • Masonry in the Americas Aztec, Mayan and other Indian cultures relied on masonry for housing and monuments. Stone veneers used by Mayans at Uxmal in 9th century. Slight outward lean of these buildings made them appear light and elegant. Pueblo Bonito housed up to Pueblo Bonito 1000 residents. Chaco Canyon, NM Anasazi constructed 10th Century AD multistory pueblos from stone, covers more than 3 acres mud and beams during period of 1100-1300 AD. Masonry Structures, Lectures 2-3, slide 9 Romanesque, Gothic and Renaissance With Romanesque architecture (10th to 12th century), large internal spaces were spanned with barrel vaults supported on thick, squat columns and piers. Gothic architecture (12th to 16th century) used a pointed arch which minimized outward thrust and resulted in lighter and thinner walls. Santa Maria degli Angeli Renaissance architecture was Firenza, Italy influenced by the round arch, constructed 1420-61 AD the barrel vault, and the dome. 39 m. in diameter, 91 m. high Filippo Brunelleschi Masonry Structures, Lectures 2-3, slide 10
  • Masonry at the Turn of the Century URM brick bearing-wall construction used for multistory buildings. Design based on empirical rules. URM construction popular for low-rise buildings in inner core of cities, many of which are still standing today. In 1908, the Nat. Assoc. of Cement Users developed the first specification for concrete block. Fifty million cmus produced in 1919 which grew to 467 million in Monadnock Building 1941. Chicago, 1891 D. Burnham and J. Root Masonry Structures, Lectures 2-3, slide 11 Rational Structural Design Masonry compressive strength standardized by 1910. Empirical design still prominent through first half of twentieth century. Research on structural masonry done at the Structural Clay Products Association and Portland Cement Association. BIA in the 1966 and NCMA in 1970 developed standards for structural code of Hammurabi design of brick and block. Babylon, 1780 BC Masonry Structures, Lectures 2-3, slide 12
  • Recent Code Developments TMS developed first standard for brick/block masonry, and became Chapter 24 of 1985 UBC. Further revised in 1988, 1991 and 1994 (as Chapter 21). ACI-ASCE 530 code published in 1988. Further revised in 1992 and 1995 as MSJC code. Strength design introduced into 1985 UBC. New chapter on strength design in 2002 MSJC. MSJC Building Code Requirements for Masonry Masonry Structures, Lectures 2-3, slide 13 Masonry Seismic Provisions Chapters 8 and 8A of NEHRP Recommended Seismic Provisions for New Buildings (FEMA 222A, 1994) Appendix C of NEHRP Handbook for Seismic Evaluation of Existing Buildings (FEMA 178, 1992) FEMA 273/356 Guidelines for Seismic Rehabilitation of Buildings NEHRP Provisions for New Buildings Masonry Structures, Lectures 2-3, slide 14
  • Present Applications The use of masonry as a structural material has been developing rapidly in the western US over the last two decades. Tall buildings of structural masonry are now being constructed. A slow revolution in the Excaliber Hotel, Las Vegas east. tallest building of structural masonry URM still used for new construction. Tall, slender walls compete with tilt-up construction. Masonry Structures, Lectures 2-3, slide 15 Masonry Compressive Strength Masonry Structures, Lectures 2-3, slide 16
  • Mechanics of Masonry in Compression P = y l A P zb xb masonry unit tj xb stresses shown for zb tb mortar > unit y y zm xm mortar P xm zm y Masonry Structures, Lectures 2-3, slide 17 Biaxial Strength of Masonry Units flat-wise compressive strength of unit from test fut y compression fut brick splits when: y fut xb = f 'udt (1 ) f 'ut direct tensile strength of unit from test fudt xb tension fudt fudt Masonry Structures, Lectures 2-3, slide 18
  • Biaxial Strength of Mortar fjt mortar crushes when: - f' uniaxial compressive y jt xm = strength from test 4.1 y compression fjt 4.1 1.0 y multiaxial f' jt compressive xm xm strength xm compression y Masonry Structures, Lectures 2-3, slide 19 Masonry Compressive Strength equilibrium relation: P xb( tbl ) = xm( t jl ) tj xb = xm tb tj if mortar crushes: tb ( y f ' jt ) xm = or 4.1 t j / tb t j / tb xb = ( y f ' jt ) = ( y f ' jt ) where = 4.1 4.1 P if brick splits: y xb = f 'udt (1 - ) f 'ut Masonry Structures, Lectures 2-3, slide 20
  • Masonry Compressive Strength if mortar crushes and brick splits simultaneously: y ( y f ' jt ) = f'udt (1 ) f ' ut f'udt y f' jt = f'udt y f'ut f ' +f ' jt y = udt Hilsdorf equation f 'ut f 'udt +f 'ut y f'm = prism strength = Uu where Uu = coefficient of non-uniformity (range 1.1 to 2.5) Masonry Structures, Lectures 2-3, slide 21 Nonlinear Mortar Behavior y 1000 psi triaxial test y zm 30 psi = xm = xm xm zm zm y v y 1000 psi l x 30 psi z Masonry Structures, Lectures 2-3, slide 22
  • Unit Splitting vs. Mortar Crushing Linear Mortar y mortar unit stress path stress path fut mortar failure envelope unit mortar crushes failure fjt envelope failure compression tension xb xm fudt Masonry Structures, Lectures 2-3, slide 23 Unit Splitting vs. Mortar Crushing Nonlinear Mortar y unit fut stress path mortar failure unit splits envelope unit fjt mortar failure stress path envelope failure compression tension xb xm fudt Masonry Structures, Lectures 2-3, slide 24
  • Incremental Lateral Tensile Stress on Masonry Unit Assuming linear behavior for masonry unit, and nonlinear mortar behavior: Eb y b - m( xm,zm ) Ej ( xm, z m ) xb = Eb tb Eb tb - b - m ( xm,zm ) 1 + Ej ( xm, z m ) t j Ej ( xm, z m ) t j where : = Poisson s ratio for masonry unit b m = Poisson s ratio for mortar = Young s modulus for masonry unit E b E j = Young s modulus for mortar t b = thickness of masonry unit = tj thickness of mortar joint = xm , zm lateral mortar compressiv e stresses From Atkinson and Noland A Proposed Failure Theory for Brick Masonry in Compression, Proceedings, Third Canadian Masonry Symposium, Edmonton, 1983, pp. 5-1 to 5-17. Masonry Structures, Lectures 2-3, slide 25 Effect of Mortar on Compression Weaker Mortars M S y weaker mortars result in weaker prism strength because ratio of vmortar/vunit is larger N weaker mortars result in greater extents of nonlinear prism behavior O y Masonry Structures, Lectures 2-3, slide 26
  • Effect of Mortar on Compression Stronger Mortars M may not adhere to units as well. S y a larger scatter of experimental data with the stronger mortars. N create a stiffer prism which is more sensitive to alignment problems during testing and more brittle. O more variable masonry compressive strength. y Masonry Structures, Lectures 2-3, slide 27 Guidelines for Prism Testing UBC Sec. 2105.3.2: Masonry Prism Testing A set of five prisms shall be built and tested prior to construction in accordance with UBC Std. 21-17. At least three prisms per 5,000 sq. feet of wall area shall be built and tested during construction. Test values for prism strength shall exceed design values. Note that testing is not required if half of allowable stresses are used for design. NCMA TEK 18-1 Concrete Masonry Prism Testing Masonry Structures, Lectures 2-3, slide 28
  • Guidelines for Prism Testing UBC Standard 21-17: Test Method for Compressive Strength of Masonry Prisms Methods for prism construction, transportation and curing. h Preparation for testing, test procedures, etc. Calculation for compressive stress. Net area, correction factors. tp Table 21-17A prism h/tp 1.3 1.5 2.0 2.5 3.0 4.0 5.0 correction 0.75 0.86 1.00 1.04 1.07 1.15 1.22 factor Use lesser of average strength or 1.25 times least strength. Masonry Structures, Lectures 2-3, slide 29 Code Values for Prism Strength UBC Sec. 2105.3.4: Unit Strength Method Use test values per UBC 21-17. Take fm equal to 75% of average prism record value. (2105.3.3) Take fm from Table 21-D if no prisms are tested. Associated BIA Technical Note: 35 Early Strength of Brick Masonry Masonry Structures, Lectures 2-3, slide 30
  • Compressive Strength of Masonry per UBC UBC Table 21-D Specified compressive strength of clay masonry, fm Specified Compressive Strength Compressive Strength of Masonry, fm, (psi) of Clay Masonry Units (psi) Type M/S mortar Type N mortar 14,000 or more 5,300 4,400 12,000 4,700 3,800 10,000 4,000 3,300 8,000 3,350 2,750 6,000 2,700 2,200 4,000 2,000 1,600 Masonry Structures, Lectures 2-3, slide 31 Compressive Strength of Masonry per UBC UBC Table 21-D Specified compressive strength of concrete masonry, fm Specified Compressive Strength Compressive Strength of Masonry, fm, (psi) of Concrete Masonry Units (psi) Type M/S mortar Type N mortar 4,800 or more 3,000 2,800 3,750 2,500 2,350 2,800 2,000 1,850 1,900 1,500 1,350 1,250 1,000 950 Masonry Structures, Lectures 2-3, slide 32
  • MSJC Specifications for Prism Strength Sec. 1.4.B Compressive Strength Determination Sec. 1.4B.2 Unit Strength method Table 1 Compressive Strength for Clay Masonry Table 2 Compressive Strength for Concrete Masonry Sec. 1.4B.3 Prism Test Method ASTM C 1314 Masonry Structures, Lectures 2-3, slide 33 Compressive Strength of Masonry per MSJC MSJC Specification Table 1 Compressive strength of clay masonry by unit strength method Net Area Compressive Strength Net Area of Clay Masonry Units (psi) Compressive Strength of Masonry Type M/S Mortar Type N Mortar (psi) 1,700 2,100 1,000 3,350 4,150 1,500 4,950 6,200 2,000 6,600 8,250 2,500 8,250 10,300 3,000 9,900 - 3,500 13,200 - 4,000 Masonry Structures, Lectures 2-3, slide 34
  • Compressive Strength of Masonry per MSJC MSJC Specification Table 2 Compressive strength of concrete masonry by unit strength method Compressive Strength Net Area of Concrete Masonry Units (psi) Compressive Strength of Masonry Type N Mortar Type M/S Mortar (psi) 1,250 1,300 1,000 1,900 2,150 1,500 2,800 3,050 2,000 3,750 4,050 2,500 4,800 5,250 3,000 MSJC values of compressive strength from Table 1 and Table 2 are intended to be used in lieu of prism tests to estimate needed mortar types and unit strengths for a required compressive strength. Masonry Structures, Lectures 2-3, slide 35 Comparison of Default Prism Strengths UBC Table 21-D vs. MSJC Specifications Table 1 C lay-U nit Masonry 6 M/S, UBC 5 Pr is m St re ngt h, f'm ksi N, UBC 4 M /S, M SJC 3 N , M SJC 2 1 0 0 5 10 15 20 Unit Strength, ksi Default prism strengths are lower bounds to expected values. Masonry Structures, Lectures 2-3, slide 36
  • Comparison of Default Prism Strengths UBC Table 21-D vs. Table 2 MSJC-Spec. Concrete-Unit Masonry 3.5 M/S, UBC 3 M/S, MSJC N, UBC P rism Strength, f'm ksi 2.5 N, MSJC 2 1.5 1 0.5 0 0 2 4 6 8 10 Unit Strength, ksi Note: MSJC and UBC values are almost identical for concrete masonry. Default prism strengths are lower bounds to expected values. Masonry Structures, Lectures 2-3, slide 37 Masonry Elastic Modulus Masonry Structures, Lectures 2-3, slide 38
  • Elastic Modulus of Masonry in Compression Basic Mechanics j = deformation of mortar = j t j = E t j [1] y P = y Anet j t b = deformation of unit = b t b = [2] y E b b = deformation of masonry = E ( t j + t b ) y [3] m y = j + b = E t j + E tb y [4] tj j b tb t t = thickness ratio = t j [5] b E m = modulus ratio = E j [6] b t j + tb = ( 1 + t )tb [7] Masonry Structures, Lectures 2-3, slide 39 Elastic Modulus of Masonry in Compression Basic Mechanics y y from 3 and 7 : = ( t j + tb ) = ( 1 + t )tb [8] P = y Anet m m y y from 1,5 and 6 : j = t tb tj = [9] m Eb Ej y y y tj ( 1 + t )t b = t tb + [10] from 4, 8 and 9 : tb m Eb Em Eb tb (1+ t ) 1 t = +1) ( [11] Eb m Em (1+ t ) m = b t [12] (1+ ) m Reference: Structural Masonry by S. Sahlin, Section D.2 Masonry Structures, Lectures 2-3, slide 40
  • Elastic Modulus of Masonry in Compression (1 + t ) = Em t Em Emasonry Eb (1 + = ) m Eb Eunit 1.2 1.0 t= 0.152 0.8 concrete block masonry 0.76 (typical for brick masonry) t= 0.0498 0.6 clay-unit masonry (typical for concrete block masonry) 0.4 0.2 E mortar m = 0.0 E unit 0 0.5 1 1.5 2 Masonry Structures, Lectures 2-3, slide 41 Code Assumptions for Elastic Modulus UBC Sec. 2106.2.12 and 2106.2.13 & MSJC Sec. 1.8.2.2.1 and 1.8.2.2.2 secant method estimate without prism test data UBC Sec. 2106.2.12.1 for clay-unit or concrete masonry fm Em = 750 fm < 3000 ksi Em fmt MSJC Sec. 1.8.2.1.1 for clay-unit masonry Em = 700 fm for concrete-unit masonry 0.33 fmt Em = 900 fm UBC 2106.2.13 0.05 fmt MSJC Sec. 1.8.2.2.2 m G = 0.4 Em Masonry Structures, Lectures 2-3, slide 42
  • Strength of URM Bearing Walls Masonry Structures, Lectures 2-3, slide 43 Unreinforced Bearing and Shear Walls Structural Walls have 3 functions: floor or roof loads (bearing wall) resist vertical compression resist bending from eccentric vertical loads and/or transverse wind, earthquake, or blast loads ds oa e l wall) resist in-plane shear and ers in-plane sv lane bending from lateral loads ran-of-p shear and t applied to building system t moment (ou in direction parallel with (shear wall) plane of wall Ref: BIA Tech. Note 24 The Contemporary Bearing Wall Masonry Structures, Lectures 2-3, slide 44
  • Unreinforced Bearing and Shear Walls Historically walls were sized in terms of h/t ratio which was limited to 25. 2 M = wh = F S = F t 2 6 8 b b h = 8 F = 8 (50 psi) ( 144 ) 2 b t 6 w 6 (15 psf) 2 wind = 15 psf h h = 25.3 t Empirical design of masonry UBC 2105.2 h < 35 Associated BIA Technical Note: 24 series The Contemporary Bearing Wall Building Masonry Structures, Lectures 2-3, slide 45 Concentric Axial Compression Buckling Load Euler buckling load: P = y Anet Pcr = Em2I cr = Em I 2 2 ( kl ) ( kl ) A 2 for rectangular section: h = kl bt 3 A = bt I= 12 bt 3 t2 I r= = = = 0.289t A 12bt 12 t Masonry Structures, Lectures 2-3, slide 46
  • Concentric Axial Compression 3 2 m( bt ) 0 .82 m 12 = cr = 2 kl 2 y (kl) bt () t if Em =750 f 'm and h' = kl, then cr = 615 f'2m ( h' ) fm t 24.8 Euler curve cutoff at f 'm = cr = 615f'2 , or h' /t = 24 .8 m ( h' ) 615f' m cr = t ( h' ) 2 t 0.25 fm MSJC/UBC h/t 100 25 50 75 Note: for MSJC and UBC plot, r=0.289t is assumed Masonry Structures, Lectures 2-3, slide 47 Code Allowable Compressive Stress Fa MSJC Section 2.2.3 and UBC Section 2107.3.2: f 'm 0.3 for h/r < = 99: Fa = 0.25 fm [1 - (h/140r)2] MSJC Eq. 2-12 and UBC Eq. 7-39 for h/r > 99 : Fa = 0.25 fm [(70r/h)2] MSJC Eq. 2-13 and UBC Eq. 7-40 0.2 0.1 h' 0 r 0 50 100 150 200 Masonry Structures, Lectures 2-3, slide 48
  • Concentric Axial Compression UBC 2106.2.4: Effective Wall Height no sidesway restraint translation restrained h=kh h rotation rotation rotation rotation k = h/h unrestrained restrained unrestrained restrained 1.0 0.70 2.0 2.0 MSJC 2.2.3: Buckling Loads 2EmI ( 1 0.577 e )3 P 1 Pe Pe = (2 11 / 2 - 15) 4 r h' 2 e = eccentricity of axial load Masonry Structures, Lectures 2-3, slide 49 Concentric Axial Compression UBC 2106.2.3: Effective Wall Thickness C. Cavity Walls A. Single Wythe t = specified thickness both wythes loaded one wythe loaded P B. Multiwythe P1 P2 t mortar or air space grout filled collar joint wire joint reinforcement t2 t1 t2 t1 each wythe t = t1 + t 2 2 2 considered separate Masonry Structures, Lectures 2-3, slide 50
  • Concentric Axial Compression UBC 2106.2.5: Effective Wall Area Effective area is minimum area of mortar bed joints plus any grouted area. face shell raked joint effective thickness effective thickness Neglect web area if face-shell bedding is used. Masonry Structures, Lectures 2-3, slide 51 Example: Concentric Axial Compression Determine the allowable vertical load capacity of the unreinforced cavity wall shown below per both the UBC and the MSJC requirements. Pa Case A: Prisms have been tested. fm = 2500 psi for block wall 8CMU 4 brick fm = 5000 psi for brick wall face-shell metal ties bedding Case B: No prisms have been tested. 20-0 fm = 1500 psi for block wall (Type I CMUs and 7.63 Type S mortar will be specified.) 3.63 Per NCMA TEK 14-1A for face shell bedding: concrete footing Anet = 30.0 in2 Inet = 308.7 in4 r = 2.84 in. (r based only on loaded wythe) Masonry Structures, Lectures 2-3, slide 52
  • Example: Case A MSJC Section 2.2.3 & UBC 2107.3.2 h' 12( 20') = = 84 .5 r 2 .84 in. for h'/r < 99: Fa = 0 .25 f'm [ 1 (h'/ 140 r)2 ] Fa = 0 .159 f'm = 0 .159( 2500 psi) = 397 psi Pa = ( 0 .397 ksi)( 2 x 1.25 in. x 12 in.) = 11.9 kip/ft MSJC Section 2.2.3: check buckling * 2 m I 1 e ( 1 0 .577 )3 P< Pe = 0 .25 h2 4 r Em = 900 f'm MSJC Section 1.8 .2 .2 .1 Em = 900 2500 = 2 ,250 ,000 psi = 2250 ksi 2( 2 .25 x 10 3 )( 308.7 ) P = 0 .25 = 29 .8 kip/ft buckling doesn't govern ( 240 )2 Pa = 11.9 kip / ft for both codes * no buckling check per UBC. Masonry Structures, Lectures 2-3, slide 53 Example: Case B MSJC Section 2.2.3 & UBC 2107.3.2 h' 12( 20' ) = = 84.5 r 2.84 in . for h' / r < 99 : Fa = 0.25 f 'm [ 1 ( h' / 140r )2 ] Fa = 0 .159 f 'm = 0.159( 1500 psi ) = 283 psi Governs for MSJC, take 1/2 for UBC since no Pa = ( 0.283 ksi )( 2 x 1.25 in . x 12 in .) = 7.2kip / ft special inspection is provided. MSJC Section 2.2.3: check buckling 2 m I 1 e P< Pe = 0.25 ( 1 0.577 )3 h2 4 r m = 900 f 'm MSJC Section 1.8.2.2.1 m = 900 1500 = 1350,000 psi = 1350 ksi 2 ( 1.35 x 10 3 )( 308.7 ) P = 0.25 = 17.85kip / ft buckling doesn' t govern ( 240 )2 Masonry Structures, Lectures 2-3, slide 54
  • Eccentric Axial Compression e axial stress bending stress P M = Pe P Pe P Mc M fa = fb = = A I S h combined axial stress plus bending -fa + fb fa + fb t Ref: NCMA TEK 14-4 Eccentric Loading of Nonreinforced Concrete Masonry Masonry Structures, Lectures 2-3, slide 55 Eccentric Axial Compression UBC Section 2107.2.7 and MSJC 2.2.3: Unity Formula fa f limiting compressive stress + b < 1 .0 (controls for small es) Fa Fb where Fa= allowable axial compressive stress (UBC 2107.3.2 or MSJC Sec. 2.2.3) Fb= allowable flexural compressive stress = 0.33 fm (UBC 2107.3.3 or MSJC Sec 2.2.3) UBC 2107.3.5 or MSJC 2.2.3: Allowable Tensile Stress limiting tensile stress -fa + fb < Ft (controls for large es) where Ft = allowable tensile stress References Associated NCMA TEK Note 31 Eccentric Loading of Nonreinforced Concrete Masonry (1971) Associated BIA Technical Note 24B Design Examples of Contemporary Bearing Walls 24E Design Tables for Columns and Walls Masonry Structures, Lectures 2-3, slide 56
  • Allowable Tensile Stresses, Ft MSJC Table 2.2.3.2 and UBC Table 21-I Mortar Type Direction of Tension Portland Cement/Lime and Masonry Cement/Lime or Mortar Cement Type of Masonry N M or S N M or S all units are (psi) tension normal to bed joints 24 15 30 solid units 40 15 9 19 hollow units 25 41* 26* 58* fully grouted units 68* tension parallel to bed joints 48 30 60 solid units 80 30 19 38 hollow units 50 48* 29* 60* fully grouted units 80* * grouted masonry is addressed only by MSJC Masonry Structures, Lectures 2-3, slide 57 Allowable Flexural Tensile Stresses, Ft flexural tension normal to bed joints Note: direct tensile stresses across wall thickness is not allowed per UBC or MSJC. flexural tension parallel to bed joints strong units weak units No direct tensile strength assumed normal to head joints, just shear strength along bed joint. Masonry Structures, Lectures 2-3, slide 58
  • Example: Eccentric Axial Compression Determine the allowable vertical load capacity per UBC and MSJC. e = 3.0 fm = 2000 psi (from tests) Pa Type S mortar Ft = 25 psi per UBC 2107.3.5 and MSJC Table 2.2.3.2 1.25 face-shell 20-0 bedding 8CMU Per NCMA Tek 141A: ungrouted (per running foot) Anet = 30.0 in2 7.63 Ix= 309 in4 Sx = 81.0 in3 concrete footing r= 2.84 Masonry Structures, Lectures 2-3, slide 59 Example Tension controlling: - fa + fb = Ft = 25 psi Pa Pe + a = Ft h - Anet Snet Pa P ( 3 .0quot;) +a = 25 psi Pa = 6750 lbs. - 30.0 81.0 Masonry Structures, Lectures 2-3, slide 60
  • Example Compression controlling: UBC 2107.3.4 and MSJC 2.2.3 Fb = 0.333 f 'm = 0.333( 2000 psi ) = 667 psi h 12.0 ( 20' ) = = 74.8 r 2.84 in. h 2 Fa = 0.25f m 1 - 140r Fa = 0.159 f m = 0.159(2000 psi) = 318 psi Pa Pa e Pa Pa e Anet Snet 30.0 + 81.0 1.0 + 1.0 Fa Fb 318 psi 667 psi Pa = 6233 lbs . < 6750 lbs . compressio n controls Masonry Structures, Lectures 2-3, slide 61 Example MSJC Section 2.2.3: Check Buckling (no buckling check per UBC) Em = 900 f 'm per MSJC Sec. 1.8.2.1.1 3 2 Em I e 1 0.577 P < 0.25Pe = 0.25 h2 r 3 2 ( 1800 ksi)(308.7 in 4 ) 3.00 1 0.577 0.25 Pe = 0.25 (240 in)2 2.84 P < .25Pe = 1417 lbs < 6233 lbs. buckling controls Pa (lbs) Code Compression Tension Buckling 6233 UBC ----- 6750 1417 MSJC 6233 6750 Masonry Structures, Lectures 2-3, slide 62
  • Kern Distance for URM Wall Assuming Ft = 0 for solid section. e - fa + fb = 0 P P Mc + =0 - AI I = bt 3 /12 A = bt P Pe(t/2) + =0 t - bt bt 3 /12 b/3 fa e = t/6 + t t/3 kern fb = b -fa + fb = 0 fa + fb If load is within kern, then no net tensile stress. Masonry Structures, Lectures 2-3, slide 63 Kern Distance for URM Wall Specific Tensile Strength, Ft, for solid section. e - f a + f b = Ft P P Mc + = Ft - AI P Pe(t/2) -+3 = Ft b Ft b 2 t bt bt /12 + t 3 3P fa t Ft t 2 b e= + t Ft t 2 b t 6 6P kern + + 3 3P fb = b -fa + fb = Ft If load is within kern, fa + fb then tensile stress < Ft. Masonry Structures, Lectures 2-3, slide 64
  • Strength of Walls with no Tensile Strength Resultant load inside of kern. P PM [1] fm = + AS P 6 Pe t fm = + [2] bt bt 2 e P 6e fm = (1+ [3] ) bt t fm f m Fa orFb Fb = 0.33 f 'm P Masonry Structures, Lectures 2-3, slide 65 Strength of Walls with no Tensile Strength Resultant load outside of kern. Neglect all masonry in tension. Note: This approach is outside of UBC and P MSJC since Ft may be exceeded. 2P fm = = compressiv e edge stress < Fa or Fb [1] b t t = 3( e ) = e [2] t 2 3 2 t/2 2P 2P 1 fm = = b 3 b( t e ) t 2 [3] e 2 t2 3 4P fm < Fa or Fb fm = e [4] 3bt(1 - 2 ) t Partially cracked wall is not prismatic along its height. Stability of the P wall must be checked based on Euler criteria modified to account for zones of cracked masonry. Analytical derivation for this case is provided in Chapter E of Structural Masonry by S. Sahlin. Masonry Structures, Lectures 2-3, slide 66
  • Example Determine the maximum compressive edge stress. Part (a) e = 1.0 in. < t/6 = 1.27 in. within kern! P = 10 kip/ft. e P 6e 1+ fm = bt t 10,000 lbs. 6 ( 1.0 in.) 1+ = 195 psi fm = ( 12 in.)(7.63 in.) ( 7.63 in.) Part (b) e = 2.5 in. > t/6 = 1.27 in. outside of kern! t = 7.63 4P fm = e 3bt 1 - 2 two-wythe brick wall t 4 (10,000 lbs) fm = = 422 psi 2.5 in. 3( 12 in.)(7.63 in.) 1 - 2 7.63 in. Masonry Structures, Lectures 2-3, slide 67 Condition Assessment Masonry Structures, Lectures 2-3, slide 68
  • Insitu Material Properties Compressive strength Elastic modulus Flexural tensile strength Masonry Structures, Lectures 2-3, slide 69 Insitu Material Properties Shear strength Shear modulus Reinforcement P 0.75 0.75 v te + CE An = v me 1 .5 Masonry Structures, Lectures 2-3, slide 70
  • Condition Assessment Knowledge factor = 0.75 when visual exam is done Visual examination measure dimensions identify construction type identify materials identify connection types Masonry Structures, Lectures 2-3, slide 71 Condition Assessment Knowledge factor = 1.00 with comprehensive knowledge level Nondestructive tests ultrasonic mechanical pulse velocity impact echo or radiography Masonry Structures, Lectures 2-3, slide 72
  • Movements Masonry Structures, Lectures 2-3, slide 73 Differential Movements One common cause of cracking is differential movement between wythes. Different materials expand or contract different amounts due to: temperature humidity freezing elastic strain Cementitious materials shrink and creep Clay masonry expands Consider differential movements relative to steel or concrete frames shrink expand Ref: BIA Tech. Note 18 Movement - Volume Changes and Effect of Movement, Part I Masonry Structures, Lectures 2-3, slide 74
  • Coefficients of Thermal Expansion Thermal Expansion Ave. Coefficient of Linear Thermal Expansion (inches per 100 for Material 100oF (x 10-6 strain/oF) temperature increase) Clay Masonry clay or shale brick 3.6 0.43 fire clay brick or tile 2.5 0.30 clay or shale tile 3.3 0.40 Concrete Masonry dense aggregate 5.2 0.62 cinder aggregate 3.1 0.37 expanded shale aggregate 4.3 0.52 expanded slag aggregate 4.6 0.55 pumice or cinder aggregate 4.1 0.49 Stone granite 4.7 0.56 limestone 4.4 0.53 marble 7.3 0.88 Thermal coefficients for other structural materials can be found in BIA Technical Note 18. Masonry Structures, Lectures 2-3, slide 75 Moisture Movements Many masonry materials expand when their moisture content is increased, and then shrink when drying. Moisture movement is almost always fully reversible, but in some cases, a permanent volume change may result. Moisture Expansion of Clay Masonry = 0.020% Moisture Expansion of Clay Masonry = 0.020% Freezing Expansion of Clay Masonry = 0.015% Freezing Expansion of Clay Masonry = 0.015% Masonry Structures, Lectures 2-3, slide 76
  • Moisture Movements in Concrete Masonry Because concrete masonry units are susceptible to shrinkage, ASTM limits the moisture content of concrete masonry depending on the units linear shrinkage potential and the annual average relative humidity. For Type I units the following table is given. Moisture Content, % of Total Absorption (average of three units) Humidity Conditions at Job Site Linear Shrinkage, % humid intermediate arid 0.03 or less 45 40 35 40 35 30 0.03 to 0.045 35 30 25 0.045 to 0.065 Masonry Structures, Lectures 2-3, slide 77 Control Joints in Concrete Masonry Control joints designed to control shrinkage cracking in masonry. Spacing recommendations per ACI for Type I moisture controlled units. Vertical S pacing of Joint Reinforcement Recommended control None 24 16 8 joint spacing Ratio of panel length 2 2.5 3 4 to height, L/h Panel length in feet 40 45 50 60 (not to exceed L regardless of H) Cut spacing in half for Type II and reduce by one-third for solidly grouted walls. Masonry Structures, Lectures 2-3, slide 78
  • Control Joints in Concrete Masonry Control joints should be placed at: all abrupt changes in wall height all changes in wall thickness coincidentally with movement joints in floors, roofs and foundations at one or both sides of all window and door openings Masonry Structures, Lectures 2-3, slide 79 Control Joint Details for Concrete Masonry paper grout fill control joint unit raked head joint and caulk Ref. NCMA TEK 10-2A Control Joints in Concrete Masonry Walls Masonry Structures, Lectures 2-3, slide 80
  • Expansion Joints in Clay Masonry Pressure-relieving or expansion joints Pressure-relieving or expansion joints accommodate expansion of clay masonry. accommodate expansion of clay masonry. expansion joint Ref: Masonry Design and Detailing, Christine Beall, McGraw-Hill BIA Tech. Note 18A Movement - Design and Detailing of Movement Joints, Part II Masonry Structures, Lectures 2-3, slide 81 Spacing of Expansion Joints For brick masonry: W = [ 0.0002 + 0.0000045( Tmax Tmin )] L where W = total wall expansion in inches 0.0002 = coefficient of moisture expansion 0.0000043 = coefficient of thermal expansion L = length of wall in inches Tmax= maximum mean wall temperature, F Tmin = minimum mean wall temperature, F 24 ,000( p ) S= Tmax Tmin S = maximum spacing of joints in inches p = ratio of opaque wall area to gross wall area Masonry Structures, Lectures 2-3, slide 82
  • Expansion Joint Details for Brick Veneer Walls 20 oz. copper silicone or butyl sealant neoprene extruded plastic Masonry Structures, Lectures 2-3, slide 83 Vertical Expansion of Veneer flashing with weep holes rc beam steel shelf angle 1/4 to 3/8 min. clearance concrete block compressible filler joint reinforcement or wire tie clay-brick veneer Masonry Structures, Lectures 2-3, slide 84
  • Expansion Problems In cavity walls, cracks can form at an external corner because the outside wythe experiences a larger temperature expansion than the inside wythe. sun Masonry Structures, Lectures 2-3, slide 85 Expansion Problems Diagonal cracks often occur between window and door openings if differential movement is not accommodated. Masonry Structures, Lectures 2-3, slide 86
  • Expansion Problems Clay-unit masonry walls or veneers can slip beyond the edge of a concrete foundation wall because the concrete shrinks while the clay masonry expands. As a result, cracks often form in the masonry at the corner of a building. Brick Veneer Concrete Foundation Masonry Structures, Lectures 2-3, slide 87 Expansion Problems Brick parapets are sensitive to temperature movements since they are exposed to changing temperatures on both sides. Elongation will be longer than for wall below. sun parapet roof Masonry Structures, Lectures 2-3, slide 88
  • End of Lessons 2 and 3 Masonry Structures, Lectures 2-3, slide 89