Ductile Design

Ductility is the ability of a structure, its components, or the materials used therein, to maintain resistance in the inelastic domain of response. It includes the ability to sustain large deformations and the capacity to absorb energy by hysteretic behavior. Displacement ductility is defined as the ultimate strain of the material divided by its yield strain. For an anchor in tension, it may be taken as the elongation of the anchor at maximum tension load divided by the elongation at yield. 

FOR ALTERNATIVE a THE RESISTING SHEAR IS CALCULATED FOR THE TOTAL NUMBER OF ANCHORS (IN THIS CASE 12 ANCHORS) TIMES THE STRENGTH OF 

CALCULATE THE BREAKOUT STRENGTH OF ANCHORS IN SHEAR) REFERENCE ACI 318 SECTION D.6.2. 

Anchor ductility is desirable for preventing brittle failure in the connection for two reasons 1) It provides greater margin against failure because it permits redistribution of load to adjacent anchors and 2) It reduces the maximum dynamic loads by energy absorption and reduction in stiffness. (Refer to ACI 349.) An anchor that is to be characterized as a ductile element should be shown by calculation to have adequate stretch length that is compatible with the ductility required. (See 3.11.5 for an example of how to do this.) 

Note ACI318 requires that the anchor material in a ductile anchor have an elongation of at least 14 percent and a reduction of area of at least 30 percent during a tensile elongation test. See Table 2.1 for guidance on ductile material selection. For a discussion of ductility ofpost-installed anchors, see 4.5.3. 

---

Ref. [27] presents a thorough discussion of limits to structural components strengths, and these should be observed. Ductile design practices should be used. The maximum allowable design stress should not exceed 25% of the ultimate strength. The strength of the enclosure should exceed the vent relief pressure by at least 0.35 psi. 

To ensure adequate seismic safety, ductile design should be effected and gradual and detectable failure modes should be incorporated. The following measures are a sample, indicative of what should be considered at the design... 

Headed anchor rods may be used in heu of headed studs to increase the embedment and assure ductile design, or if studs are not available. Design is similar to that for headed studs. The user must ensure that the anchor rod is made of a weldable material. 

If, as in the case of a column pedestal, there is insufficient concrete to resist the tension or shear, reinforcing steel can be designed as anchor reinforcement. (See 3.5.) This can be considered a ductile design since both the anchor and the reinforcing steel are ductile. 

Low seismic risk and ductile design is not considered (Seismic design category A or B)... 

If the ductile design (which is not considered herein) is performed, the puloul resistance oMhe anchor in tension should be laiger than the tensile capacity of the anchor (i ij N g). 

Even though it is not required when ductile design is not peifonned, it is a good practice to have N b failure is not governed by a norvductile side- ce bloworff... 

Determine the required number of vertical rebar to resist Nug = 20 kip Note Ductile design is not considered (low seismic risk)... 

Brtmeau M, Uang C-M, Sabelli R (2011) Ductile design of steel structures, 2nd edn. McGraw Hill, New York... 

Properly designed modem steel stmctmes can provide superior performance when subjected to very large earthquake motions. The key to good performance is in strict attention to detail in every phase of the constraction process (a) initial selection of the stractural form (b) ductile design of members, particularly with respect to plastic hinge formation (c) careful attention to connection strength and ductility (d) frequent... 

---