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## Axial Members

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**Axial Members**WORKSHEET 11 to answer just click on the button or image related to the answer let's go !!**compression structures**tension structures a b Question 1a are tension structures or compression structures more efficient when loaded axially?**they are not subject to buckling**they are usually made of steel they pull straight they are stronger a b d c Question 1b why are tension structures more efficient?**a column which looks short**a fat column a column which will fail in true compression a b c Question 2a what is meant by a short column?**a column which looks long**a thin column a column which buckles before its full compressive strength is reached a b c Question 2b what is meant by a long column?**the moment of inertia, I**the modulus of elasticity, E the maximum allowable compressive strength the slenderness ratio the end fixing conditions b, c and d b, d and e a b d e g c f Question 3 what affects the buckling load?**I-sections**sections with similar radii of gyration in all directions rectangular sections sections in which the major part of the material is as far from the Centre of Gravity as possible b and d a b d e c Question 4a what are good sections for columns?**why are these good sections for columns?**they are cheaper so that they do not buckle in the weak direction they use the material more efficiently a and c a, b and c a b d e c Question 4b similar radii of gyration in all directions and material far away from the Centre of Gravity**bad construction**a horizontal load an eccentric vertical load b and c a b d c Question 5 what are two effects which can cause a pier to overturn?**the force acting on the pier being in**the middle third of the pier the resultant reaction being in the middle third of the base a b Question 6a does the middle third rule deal with?**the pier will not overturn**no tension will develop in the base of the pier the pier will not lift off its base b and c a and b a b d e c Question 6b if the middle third rule holds, what does that tell you?**the safety factor is > 3**the safety factor is 3 the safety factor is 2 a b c Question 6c if the middle third rule holds, what does that tell you about the safety factor?**300**1000 8kN 1kN 1.6 kNm 1.0 kNm 1.3 kNm Pier 600 x 600mm a b c Question 7a a heavy steel gate is hung from a hollow brick pier as shown in the diagram what is the overturning moment?**300**1000 8kN 1kN 2.4 kNm 4.8 kNm 8 kNm Pier 600 x 600mm a b c Question 7b a heavy steel gate is hung from a hollow brick pier as shown in the diagram what is the stabilizing moment?**300**1000 8kN 1kN yes, the weight of the gate is eccentric no, the weight of the pier is greater than the weight of the gate yes, the overturning moment is greater than the stabilizing moment no, the stabilizing moment is greater than the overturning moment Pier 600 x 600mm a b d c Question 7c a heavy steel gate is hung from a hollow brick pier as shown in the diagram will the pier overturn and why or why not?**300**1000 8kN 1kN 2 : 1 2.4 : 1 3 : 1 > 3 : 1 Pier 600 x 600mm a b d c Question 7d a heavy steel gate is hung from a hollow brick pier as shown in the diagram what is the margin of safety?**300**1000 8kN 1kN 8 kN 9 kN 2.4 kN Pier 600 x 600mm X R a b c Question 7e a heavy steel gate is hung from a hollow brick pier as shown in the diagram what is the value of the vertical reaction, R?**300**1000 144.4 mm 155.6 mm 377.8 mm a b c Question 7f a heavy steel gate is hung from a hollow brick pier as shown in the diagram 8kN 1kN what distance is the vertical reaction from X? h =? Pier 600 x 600mm X R = 9 kN h**300**1000 yes no a b Question 7g a heavy steel gate is hung from a hollow brick pier as shown in the diagram 8kN 1kN is the reaction in the middle third of the base? Pier 600 x 600mm X R = 9 kN 144.4 mm h = 155.6 mm**300**1000 you can’t tell no yes a b c Question 7h a heavy steel gate is hung from a hollow brick pier as shown in the diagram. The reaction is outside the middle third. 8kN 1kN Pier 600 x 600mm is this what we would expect from our previous observations? X R = 9 kN 144.4 mm h = 155.6 mm**300**1000 (0.020 +/- 0.027) MPa (0.020 +/- 0.036) MPa (0.025 +/- 0.036) MPa a b c Question 7i a heavy steel gate is hung from a hollow brick pier as shown in the diagram. The reaction is outside the middle third. 8kN 1kN Pier 600 x 600mm what is the stress distribution under the pier? X R = 9 kN 144.4 mm h = 155.6 mm stress = P/A ±Pe/Z Z = bd2/6**300**1000 yes no not possible to tell a b c Question 7j a heavy steel gate is hung from a hollow brick pier as shown in the diagram. The pier is developing tension on the left-hand side. 8kN 1kN Pier 600 x 600mm is this what you would expect? X R = 9 kN 144.4 mm h = 155.6 mm**300**1000 not possible to know no yes a b c Question 7k a heavy steel gate is hung from a hollow brick pier as shown in the diagram. The pier is developing tension on the left-hand side. If you make the pier solid, i.e. it will be about twice as heavy 8kN 1kN Pier 600 x 600mm will it be safer? X R = 9 kN 144.4 mm h = 155.6 mm**115**115 self weight 1200mm 5.24 kN 52.4 kN 52.4 kPa 600 wind 0.5kPa A R x h b a c Question 8a A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa what‘s the weight of the wall (for 1 m length)?**115**115 self weight 1200mm 0.5 kN 0.6 kN 0.6 kPa 600 wind 0.5kPa A R x h b a c Question 8b A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa what‘s the total wind force (for 1 m length)?**115**115 1200mm 5.30 kN 5.24 kN 5.74 kN 600 wind 0.5kPa A R x h a b c Question 8c W = 5.24 kN A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa what‘s the value of the reaction (for 1 m length)?**115**115 1200mm 68.7 mm 46.3 mm 183.8 mm 600 wind 0.5kPa A R = 5.24 kN x h a b c Question 8d W = 5.24 kN A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa what‘s the distance, h, of the reaction from the centre of the pier?**no**maybe yes a b c Question 8e W = 5.24 kN A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa 115 115 115 115 wind 0.6 kN 1200mm 1200mm 600 600 is the reaction within the base? A A R = 5.24 kN x x h = 46.4 mm h**tension develops on the RHS**the pier will not overturn no tension develops on the RHS the pier will overturn d a b c Question 8f W = 5.24 kN A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa The reaction is within the base 115 115 115 115 wind 0.6 kN 1200mm 1200mm 600 600 A A what does that mean? R = 5.24 kN x x h = 46.4 mm h**yes**no maybe a b c Question 8g W = 5.24 kN A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa 115 115 115 115 wind 0.6 kN 1200mm 1200mm 600 600 is the reaction within the middle third of the base? A A R = 5.24 kN x x h = 46.4 mm h**tension develops on the RHS**the pier lifts off its base a and b the pier overturns d a b c Question 8h W = 5.24 kN A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa The reaction is not in the middle third 115 115 115 115 wind 0.6 kN 1200mm 1200mm 600 600 A A what does that mean? R = 5.24 kN x x h = 46.4 mm h**400 mm**450 mm 410 mm a b c Question 8i W = 5.24 kN A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa 115 115 115 115 wind 0.6 kN 1200mm 1200mm 600 600 how wide would the footing have to be for the reaction to fall within the middle third of the base? A A R = 5.24 kN x x h = 46.4 mm h**no idea**make the wall thicker show me a b c Question 8j W = 5.24 kN A freestanding garden brick wall is 230 mm thick and 1200 mm high. The density of brick is 19 kN/m3. The wind load is 0.5 kPa 115 115 115 115 wind 0.6 kN 1200mm 1200mm 600 600 how else could we increase the stability of the wall? A A R = 5.24 kN x x h = 46.4 mm h**enough !**next question Off to a Good Start !! tension structures are more efficient**let me try again**let me out of here Sorry what’s the problem with compression structures?**enough !**next question you've got it it!! Yep! No buckling! Can use all its strength !!**let me try again**let me out of here No, That's not it ! they may be made of steel but then again they may be made of other materials**let me try again**let me out of here No, That's not it ! they do pull straight but so what?**let me try again**let me out of here No, That's not it ! some materials are stronger in compression some materials are equally strong in compression and tension so what is it about compression that may lead to early failure?**enough !**next question terriffic !! it does probably looks short and fat but the technical answer is that it fails in true compression**let me try again**let me out of here That may be true but it’s not really the answer**enough !**next question terriffic !! it does probably looks long and thin but the technical answer is that it fails in buckling before true compression**let me try again**let me out of here That may be true but it’s not really the answer**enough !**next question Fantastic the ease of buckling is a function of the slenderness ratio, the modulus of elasticity and the end restraints the slenderness ratio takes into account the effective length and the radius of gyration which takes into account the Moment of Inertia. The greater the slenderness ratio, the more likely buckling will occur. Materials with a higher Modulus of Elasticity, E, will less likely buckle. The more restrained the ends, the less likely to buckle.**let me try again**let me out of here No, No, No !! buckling is not a function of the maximum allowable compressive stress. Buckling doesn’t allow the element to reach its maximum allowable stress**let me try again**let me out of here Partly ! but it is affected by other things too**let me try again**let me out of here Not Exactly ! the Moment of Inertia figures in it but as part of something else**next question**enough ! Yipee !! you’ve got it !!**let me try again**let me out of here No, No, No !! think again – why are I-sections or rectangular sections not good for columns**let me try again**let me out of here Partly Right !