The document discusses various masonry design codes and philosophies. It explains that limit states design (LSD) is considered the most rational as it considers both safety under ultimate loads and serviceability under service loads, unlike working stress method (WSM) and ultimate load method (ULM). LSD has been adopted by most modern codes like ACI, IBC, and Eurocode. The document then discusses provisions for axial load, shear, and other limit states in different codes based on LSD and allowable stress design (ASD) formats.

1. Dr. A. Meher Prasad Department of Civil Engineering Indian Institute of Technology Madras email: prasadam@iitm.ac.in MASONRY CODES OF PRACTICE

4. Design Philosophies … “ Limit states design” is supposed to be the most rational design philosophy. Why?

6. WSM and ULM WSM attempts to ensure adequate safety under service loads, while ULM attempts to ensure adequate safety under extreme loads. WSM does not investigate behaviour beyond service loads, ULM does not guarantee serviceability under service loads.

7. Limit States Method (LSM) A limit state is a state of impending failure , beyond which a structure ceases to perform its intended function satisfactorily, in terms of either strength or serviceability ; i.e., it either collapses or becomes unserviceable . Unlike WSM , which bases calculations on service load conditions alone, and unlike ULM , which bases calculations on ultimate load conditions alone, LSM aims for a comprehensive and rational solution to the design problem, by considering safety at ultimate loads and serviceability at working loads . LSM is described as a ‘semi-probabilistic’ method or a ‘Level I reliability’ method

8. Strength Design Model pdf S n R n R and S are independent random variables Probabilistic approach: nominal / characteristic values (deterministic) Moral: There is always a risk of failure. No structure is 100% safe! R  S  Structure will survive! R < S  Structure will fail!

9. F s = R n / S n P f = Prob [ R < S ] Reliability = Probability of survival = 1 - Probability of failure pdf S n R n Deterministic measure of safety: Probabilistic measure of safety: f S ( s ) f R ( r ) = Prob

10.  R k   S k Load and Resistance Design (LRFD) Format Design Resistance  Design Load Effect  S n R n  S n =  R n Load factor > 1 (‘overloading’) Resistance factor < 1 (‘understrength’)  (ULM format)  (WSM format)

11. Partial load and material safety factors Ultimate limit states – partial load factors: UL = 1.5 (DL + LL) UL = 1.5 (DL + QL) or (0.9DL + 1.5 QL) UL = 1.2 (DL + LL + QL) Note : It is not correct to apply 33.3% increase in allowable stress in WSM when only DL and QL are involved! Ultimate limit states – material safety factors : Concrete: = 1.5 Steel: = 1.15

20. IS 1905 :1987: a stress reduction factor k s which depends on slenderness ratio and eccentricity of load (Table 9 of Code) Slenderness effects on axial compression Axial Compression - ASD

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22. Slenderness ratio for different Eccentricities

23. Reinforced Masonry Axial Compression - ASD ACI 530-02 IBC 2000, NZS:4230: Part 1 , Eurocode 6, IS: 1905-1987 No Provisions have been given

24. Maximum h/t Ratio There is no directly specified limit to the h/t ratio. It is indirectly specified through the check against Euler’s buckling formula ACI 530-02 IS: 1905-1987 Maximum h/t ratio depends on the storey height and type of mortar used. IBC 2000, NZS:4230: Part 1 , Eurocode 6 No Provisions have been given

26. Interaction formula Very conservative Axial compression with flexure: ASD

27. Axial compression with flexure: ASD Significance of M/Vd v factor

31. Axial compression with flexure Flexure and Axial Wall Loading Interaction Diagram Reinforced Masonry

32. Design for Shear – ASD ACI 530-02 Shear stress shall not exceed either of 0.125 , 0.83MPa or v+0.45N v /A n IBC 2000, NZS:4230: Part 1 , Eurocode 6 No Provisions have been given IS: 1905-1987 Permissible shear stress is given by: F v = 0.1 + /6 < 0.5MPa Un Reinforced Masonry

33. If shear reinforcement is not provided ACI 530-02 For flexural members, For shear walls, a. M/Vd v < 1, F v = 0.028[4-M/Vd v ] < (0.55-0.31M/Vd v )MPa b. M/Vd v > 1, F v =0.083 < 0.24MPa F v = 0.083 < 0.35MPa, IBC 2000, NZS:4230: Part 1 , Eurocode 6, IS: 1905-1987 No Provisions have been given Design for Shear – ASD Reinforced Masonry

34. ACI 530-02 For flexural members, Fv = 0.25 < 1.03MPa For shear walls, a. M/Vd v < 1, Fv = 0.042[4-M/Vdv] < (0.82-0.031M/Vdv)MPa b. M/Vd v > 1, Fv = 0.125 < 0.52MPa If shear reinforcement is provided Design for Shear – ASD Reinforced Masonry

35. IS: 1905-1987 Permissible shear stress is given by: Fv = 0.1 + /6 < 0.5MPa IBC 2000, NZS:4230: Part 1 , Eurocode 6 No Provisions have been given ASD format If shear reinforcement is provided Design for Shear – ASD Reinforced Masonry

39. IS 1905:1987: takes care of sliding failure by specifying permissible shear stress URM Average axial stress not more than 2.4 MPa

40. Allowable shear for reinforced walls

43. Capacity Design for strength of flanged wall

44. Effective Shear Areas

45. LSD

46. AXIAL COMPRESSION - LSD Un Reinforced Masonry: ACI 530-02 IS: 1905-1987, NZS:4230: Part 1 IBC 2000 Eurocode 6 Charactersistic Compressive strength of Masonry is Maximum compressive strain is limited to 0.002 No Provisions are given

47. Reinforced Masonry: ACI 530-02 Eurocode 6, IS: 1905-1987 No Provisions are given AXIAL COMPRESSION - LSD IBC 2000 NZS:4230: Part 1

48. AXIAL COMPRESSION WITH FLEXURE - LSD Un Reinforced Masonry: ACI 530-02, IBC 2000, NZS:4230: Part 1, IS 1905- 1987 No Provisions are given Eurocode 6 1. Design Md equals 2. In case of vertical load, increases to 3. Lateral resistance

49. AXIAL COMPRESSION WITH FLEXURE - LSD Reinforced Masonry: ACI 530-02 2. For walls with factored axial stress < 0.2f m , 1. For walls with factored axial stress < 0.05f m , and SR > 30 shall be designed as above with walls having t min =150mm. 3. at extreme fiber is 0.0035 for clay masonry and 0.002 for concrete masonry.

50. AXIAL COMPRESSION WITH FLEXURE - LSD Reinforced Masonry: IBC 2000 1. For wall design against out-of-plane loads, all values are same as of the ACI code, except 2. is the same as in the ACI code. NZS:4230: Part 1 1. is 0.0025 for unconfined concrete masonry and 0.008 for confined concrete masonry Eurocode 6 For singly reinforced rectangular c/s subjected to bending only IS 1905- 1987 No provisions

53. DESIGN FOR SHEAR - LSD Reinforced Masonry: NZS:4230: Part 1 1. Shear strength is given in section 7.3.2.1 2. Minimum value of A v = 0.15 b w s/f y 3. 4. Required area of shear friction reinforcement is Eurocode 6 1. Ignoring shear reinforcement: 2. Taking shear reinforcement into account: IS: 1905-1987 No Provisions