Bending moment on the bottom beam doesn't look quite right. It implies theres a vertical tension restraint on the "springs". You need to make them non linear springs with no tension stiffness. Similar happens when you model a larger raft at braced bays. It would be good if you went through a hand calc either before or after to verify the results and show that you don't always need a computer program. Edit: Also watch your units for, spring stiffness…… kN/m/m in your calc but kN/m Tekla input. Your 1d elements are 1.25m long so if I’m not mistaken your spring stiffness would be 50[kN/m]*1.25[m]/0.02[m]=3125kN/m for along the span and 3125/2 for the ones below the column.

Are the springs modeled to only restrain compression in Tekla, allowing for the beam to uplift? I would expect the bending moment diagram to look different for the bottom beam?

@Aaron-gl8cm

2 жыл бұрын

I agree, it should look more like an upside-down simply supported beam. You would need to use non linear springs to eliminate that restraint.

@puktoon100

Жыл бұрын

@@Aaron-gl8cm Hi , just saw you comments. IF i were try this with non linear stiffness. it is asking for positive stiffness and FMax( which assume is the maximum Axial force?).

Very well explained as always.

Show a typical domestic box frame design next please 💪

Hey, can you do a video on how you would detail these connections? Especially when installing these in a house

Great video. Would love to watch more projects working on TSD software from you.

Hi Dazz, brilliant video with a very common scenario in domestic structural engineering. As a new entrant into the domestic market could you advise if the bottom beam of the steel Box could be positioned on the Rising Wall (usually solid concrete blocks on the flat) rather than the existing strip foundation? Positioning the bottom steel on the rising wall would be more beneficial to the client/builder as there would be more reuse of the existing structure, and less demolition waste. The load spread at the base indicates that loads are approx 35Kn at each spring position, therefore the rising wall would be modeled with a UDL of 35Kn/m and this loading can be easily carried by the rising wall. thanks

When designing a goal post frame do you use a tie rod below the opening to restrain the base of the columns from 'kicking out' or do you design the foundations to take the horizontal loading. I normally design with a tie at ground floor level but I have recently had queries from Architects saying that other Structural Engineers do not put these in. If you design the foundations to take the horizontal load it can make the pad foundations quite large! Just wondering what you would normally do.

Hi Daz, I was really looking forward to box frame design and this is good. I normally design box frame the option 2 way and i would expect to behave similar on the ground level with stiffer section due to being encased in concrete. I would you use same bending moment as the top member for connections. if you add lateral loads then it will give you error which basically they will ask you restraint it one direction on top level.

@ivandimitrov3043

Жыл бұрын

Hi SS, do you refer to the simple beam on columns option? I would say what type of support you use depends on the connection detail. If the ends of the beam are fixed, there is no issue with the lateral loads. If you used fixed supports for the top beam, wouldn't the bottom of columns be fixed as well, as it will probably be the same connection detail as the top of the columns?

Genuinely don't know if I'm right in saying the below, just going from my own logic and asking the question. Is spring stiffness not a property of the soil as opposed to a property of the load? Also, if you have units of kN/m divided by metres, you will surely get kN/m^2? My thought would be that if the ground bearing pressure were 150kN/m^2 for example, and the deflection was 20mm, then the spring stiffness would be 150 x 0.02 = 3kN/m?

@user-ut9hl4bx7i

4 ай бұрын

I have since found out the correct solution from "Foundation Analysis and Design" 5th edition by Bowles (pages 501 and 513). The value shown in your video needs to be multiplied by the width of foundation and the trib length for each node. This will give you your value in kN/m, which is correct for a value of spring stiffness.

thanks

Great video Daz. Not easy posting to the world! If it sparks discussion, that’s a good thing as that’s what we do in the office! Constructive comments here. Great stuff, please keep it up.

Which software are you using for box frame analysis?

@EverydayDazz

2 жыл бұрын

I used tekla structural designer for this example but most modern analysis software can do it

New subs from Mat Picardal YT channel

Box frame may be higher in the construction cost compared to simple support however, you explain it pretty good