Columns and Beams
From Bottle School Wiki
- The columns and beams are the load-bearing, structural integrity of a bottle school. Their proper assembly and pour are essential to a sound and secure building
- These columns and beams are designed for a single story construction, but columns of sufficient strength could be made for multiple floors
- Measurements for the rebar to use in each column, as well as the joints in the column, depend on the size of the column. Depending on the particular construction plans you use, some may use braces of 1/4” with iron of 3/8”, and other may use 3/8” braces with 5/8” iron. As always, check your construction plans (which have been rigorously tested and approved by a structural engineer) to ensure you use the correct thickness of rebar.
- Make sure that you center each column with regard to measurements on the constructions plans, and with regard to the footing.
- Do not forget to add pins to all necessary places on your columns and beams. You will not be able to install the chicken wire without your pins!
- 3/8” rebar is formed with 1/4” rebar ribs to contract the steel cage that will reinforce the pour concrete. They are tied together with tie wire at varying intervals
- Joints of 1/4in rebar ties need to rotate 90o every tie
- 1/4” rebar ribs are bent to form a 10cm x 10cm square in which the four 3/8” rebar will rest
- Ribs are placed every 15cm, rotating joint 90o with every subsequent rib
- 1/4” ribs are spaced every 20cm.
- Again, rotate joint 90o every rib, following in a spiraling pattern
- When it is necessary to join two 3/8in rebar sections there needs to be a minimum of a 30cm overlap
- Rounding corners, you need to have that same 30cm overlap on both sides of the corner
- Plan ahead to ensure a strong overlap in the corners
After the foundation is set it's time for the floor beam
- Form rebar cage in place, tying in with the exposed column rebar cage
- Place forms around rebar cage, ensuring 2.5cm of space on all sides (bottom, left, and right); Small rocks can be handy spacers. Drill holes for pins and place them so that they will sit vertically on the top of your floor beam and they face out horizontally on the outside face of your future wall.
- Pour in concrete
- Agitate with a trowel to remove pockets of air
- Allow to cure before removing forms advancing on to the columns
Your rebar cage will already be tied and ready to go, protruding from the recently poured floor beam
The objective here is to make the column the height of the intermediate beam (with out plans that is an additional 1.4m above the floor beam to the bottom of the intermediate)
- Put forms in place, again, ensuring proper spacing (2.5cm on all 4 sides). Drill holes for pins and place pins so that they face inward sticking out horizontally (this will be the inside of your wall where the bottles will be placed). The pins also need to stick out horizontally from the outside of your wall in your columns.
- Pour concrete
- Agitate mixture inside forms to eliminate air pockets (A piece of rebar works well. Similar to bottle stuffing, actually)
- Brace form with boards or poles to keep the column straight
- Adjust with a level or plumb until straight. Secure braces
- Allow to cure before removing forms and moving on to the intermediate beam
The intermediate beam is constructed in the same fashion as the floor beam, only this time you'll need to place forms on the underside of the rebar cage
- Place bottom form (15cm width)
- Nails can be driven into the column with small wood support to hold the form
- Drill holes for pins and place pins so that they face downwards vertically on the inside of your future wall (the bottom of your intermediate beam) and they need to stick out horizontally on the outside portion of your column (facing the outside of your classroom).
Columns and Lintel for Door
Column From Middle Beam to Lintel
- Place forms around the column's rebar cage, like before, to the height desired for the door
- Pour concrete and allow to cure
Lintel and remaining columns
The lintel and remaining columns can be poured together
- To form the lintel add a new rebar cage connecting the two columns on either side of the door
- Bend the 3/8in rebar to hook around the rebar of the column
- Outside form will need pins like the other beams
- Drill holes and insert pins. Be sure to not insert pins on the face of the columns that make up the interior of your door since you will not be placing chicken wire there. It is very important to sort out where your door will be before breaking ground to avoid any confusion over where to place pins.
- Once cement is poured, leave pins above the lintel in the same fashion as the other beams
- Above the lintel repeat the process for forming the columns
- This column section will be level with the other columns prior to prepping the top beam
- These forms will need to have holes on the inside and outside (or where bottles will be placed)
- Once rebar is securely tied and forms are in place the lintel and the remaining column can be poured
When mixing cement and concrete, it is vital that you use the correct ratios of cement, sand and gravel. Compromising this will severely affect the strength and durability of the finished school. We recommend using the ratios in the following table: