Calculating the Deflections of Stainless Steel Beams
The non-linear material stress-strain curve of stainless steel (refer to Comparison of structural design in stainless steel and carbon steel) implies that the stiffness of a stainless steel component varies with the stress level, the stiffness decreasing as the stress increases. Consequently, deflections are greater than what you would expect with carbon steel. It is therefore necessary to use a reduced modulus to predict the deflection of stainless steel members in which high stresses occur. Using standard structural theory, but with the secant modulus corresponding to the highest level of stress in the member, is a conservative method of estimating deflections in stainless steel members.
Secant modulus
The secant modulus, Es, to be used in deflection calculations should be ascertained for the member with respect to the rolling direction. If the orientation is not known, or cannot be ensured, then the lesser value of Es should be assumed. The value of the secant modulus may be obtained as follows:
where Est and Esc are the secant moduli corresponding to the stress in the tension flange and compression flange respectively. Values of Est and Esc for a given stress ratio may be read from the table below using linear interpolation as necessary.
Secant modulus at different stress levels
Stress ratio(f/py) |
Secant modulus Es (kN/mm2) |
Grade 1.4301 304 |
Grade 1.4401 316 |
1.4462 duplex 2205 |
Longitudinal direction |
Transverse direction |
Longitudinal direction |
Transverse direction |
Either direction |
0.00 |
200 |
200 |
200 |
200 |
200 |
0.20 |
200 |
200 |
200 |
200 |
200 |
0.25 |
200 |
200 |
200 |
200 |
199 |
0.30 |
199 |
200 |
200 |
200 |
199 |
0.35 |
199 |
200 |
199 |
200 |
197 |
0.40 |
198 |
200 |
199 |
200 |
196 |
0.42 |
197 |
199 |
198 |
200 |
195 |
0.44 |
196 |
199 |
197 |
199 |
194 |
0.46 |
195 |
199 |
197 |
199 |
193 |
0.48 |
193 |
198 |
196 |
199 |
191 |
0.50 |
192 |
198 |
194 |
199 |
190 |
0.52 |
190 |
197 |
193 |
198 |
188 |
0.54 |
188 |
196 |
191 |
197 |
186 |
0.56 |
185 |
195 |
189 |
197 |
184 |
0.58 |
183 |
194 |
187 |
195 |
182 |
0.60 |
179 |
192 |
184 |
194 |
180 |
0.62 |
176 |
190 |
181 |
192 |
177 |
0.64 |
172 |
187 |
178 |
190 |
175 |
0.66 |
168 |
184 |
174 |
188 |
172 |
0.68 |
163 |
181 |
170 |
185 |
169 |
0.70 |
158 |
177 |
165 |
181 |
165 |
0.72 |
152 |
172 |
160 |
177 |
162 |
0.74 |
147 |
167 |
154 |
172 |
159 |
0.76 |
141 |
161 |
148 |
166 |
155 |
Note: f is the (unfactored) stress at the serviceablilty limit state and py is the design strength, conventionally taken as the 0.2% proof strength which is 210 N/mm2 for grade 1.4301 (304) and 220 N/mm2 for grade 1.4401 (316). |
Comparison Structural Design Stainless Steel and Carbon Steel
Calculating the Deflections of Stainless Steel Beams
Structural Design of Stainless Steel
Stainless Steel Section for Structural Application
Structural Steel Comparison Table
ASTM Standards for Structural Tubing Mechanical Tubing Welded Fitting
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