cmt chapter 5

• Form


  The structural members of a building are built-up into its desired shapes and dimensions through the use of form
• Concrete Forms


  • Water tight
  • Rigid
  • Strong enough to sustain the weight of fresh concrete
• Selection of forms are based on

  • Cost of the materials
  • Construction and assembling cost
  • The number of times it could be used
  • Strength and resistance to pressure and tear and wear
• Classification of forms


  • As to materials: Wood
  • Metal
  • Plastic
  • Composite

  As to shape: Straight

  • Circular

  Solid or hollow cast: Single

  • Double

  As to methods of construction: Ordinary

  • Unit

  As to uses: Foundation

  • Wall
  • Steps
  • Beam and Girders
  • Slab
  • Sidewalk
• Types of post and wall form

  • Continuous
  • Full unit
  • Layer unit: Continuous
  • Sectional
• Construction of forms consist of

  • Retaining Board
  • Supporter or studs
  • Braces
  • Spacer
  • Tie wire
  • Bolt and nails
• Greasing of forms


  Forms are constantly greased before its use to make the wood waterproof and prevent the absorption of water in the concrete which causes swelling and warping. Crude oil is the most economical and satisfactory materials for this purpose.
• Plywood as construction form

  • Economical in terms of labor cost
  • Lightweight and handy
  • Smooth surface which may not require plastering
  • Less consumption of nails
  • Ease of assembling and disassembling
  • Available in various thickness ranging from 4; 6; 12; 20 and 25 mm with a standard commercial sizes of .90 x 1.80 and 1.20 x 2.40 meters
• In determining the materials for square and rectangular column forms, one has to consider

  • The thickness of the board to be used
  • The size of the frame
  • Types of framework to be adopted
• Formula in finding the materials for square and rectangular column forms

  P = 2 (a + b) + .20

  Multiply P by the height of one column times the number of columns to get the total area of the forms

  Divide the total area found by 2.88 to get the number of plywood forms

  Multiply the number of plywood found by 29.67 to get the board foot of frame required
• Forms for circular column

  Made of plain galvanized iron sheet or black sheets supported by vertical supports and circumferential ties
• Formula for circumferential area of circular column forms


  C = 3.1416 x diameter x Height x No. of Columns
• Forms for beam and girder

  Made of either metal or plywood materials supported by galvanized pipe staging or wooden lumber of varying sizes from 2 X 2; to 2 X 3 frames. Wooden lumber forms are rigidly supported with sufficient vertical and diagonal bracing to carry the heavy load of concrete. The ease of dismantling is the primary consideration in the assembling of forms.
• Formula in finding the materials for beam and girder form


  P = 2 (d) + b + .10

  Multiply P by the length and number of beams to get the Total Area of the forms.
• TO 2 X 4 ARE USED


  • Wooden lumber forms are rigidly supported with sufficient vertical and diagonal bracing to carry the heavy load of concrete weighing approximately 65 kilograms per cubic foot
  • The ease of dismantling is the primary consideration in the assembling of forms
  • The freedom from pain and difficulty in removing the form depends on how it was fastened
• FORMULA IN FINDING THE MATERIALS FOR BEAM AND GIRDER FORM

  1. P = 2 (d) + b + .10

  2. Multiply P by the length and number of beams to get the Total Area of the forms

  3. Divide the total area found by 2.88 to get the number of plywood terms

  4. Multiply the number of plywood found by 22 get the board foot of frame required
• Scaffolding


  Temporary wooden structure for workers during building erection or repair
• Staging


  Substantial framework built progressively as buildings rise
• The different parts of scaffolding to consider

  • Vertical support
  • Base of vertical support (as needed)
  • Horizontal member
  • Diagonal braces
  • Block and wedges
  • Nails or bolts
• Shift towards metal pipe scaffolding for durability and ease of assembly
• Challenges in sourcing traditional lumber
• Introduction of alternatives: plywood, synthetic board, metal sheet, plastic
• Balancing cost and benefits of plastic forms and exploring cost-effective alternatives
• SOLUTION


  1. SCAFFOLDING FOR COLUMNS

  2. SCAFFOLDING FOR THE BEAM
• Total length of 6 beams is 51 meters
• Factors that affect the percentage of waste of forms and scaffolding

  • - Difference in height between floors may require adjustment of the forms and vertical support
  • Difference in sizes of beams and girders requires adjustments of the forms
  • Major causes of forms and scaffolding tear and wear are the dismantling, transferring, and re-assembling operations
  • Reckless use and handling of the materials include the making of firewood and pilferages during the construction
  • Use of inferior quality lumber contributes to the high percentage of waste and risk to the workers
• Steel Pipe Scaffolding


  • - Can be used freely to prefabricate height and width according to the places and forms to install
  • Galvanized steel pipe with good strength makes durability and also leads to economical delivery and storage
• Standard scaffolding frames have 4' (1.20 M) width available in 3 different heights ranging from .90 to 1.70 M. They are useful for access platforms and concrete support works.
• Adjustable Base Jack


  Adjusts the level of scaffolding on the ground, up to 25 cm
• Adjustable U-Head


  Adjusts the level of wood bearers/joist, up to 25 cm
• Adjustable Double Prop


  Heavy duty props which can be connected by cross braces or pipe and clamps for supporting slabs or beams. Required height can be attained by using inner pipe.
• Adjustable Straight Prop


  Ideal support for beam and slab as well as bracing for wall and column
• Cross Brace


  Various spans available in 1.20m, 1.50m, and 1.80 m. Short cross brace for 1.20 and .90 frame, long cross brace for 1.70m frame.
• Joint Pin


  Connects frame one on top of the other
• Adjustable Slab Bearer


  Used on extension to hold on to slab lumber joist
• Sample Problem: Finding the number of 6mm x 1.20 x 2.40m plywood forms and corresponding frame using 2" x 2" and 2" x 3" lumber


  Calculate the number of plywood forms needed for rectangular columns

  2. Calculate the number of plywood forms needed for circular columns

  3. Add the total number of plywood forms for rectangular and circular columns
• Total number of 6mm x 1.20 x 2.40m plywood forms required = 72 + 24 = 96 forms