Project Engineers' Guide: Design

Fieldwork No. 11

While the men are working I am designing the spaces inside and outside the house. The bougainvillea walkway trellis leads to a patio at both ends. On the left side there is a cemented pavement where we dry the clothes. Right next to it is a shower room and a toilet where heavy-duty tiles separate it from the kitchen. I will show you later. Probably i will let my wife design the rest.

Okay part of being a Project Engineer is you should know how to estimate. 1 bag of cement weight 40 kg is also equivalent to a volume of 1 cubic feet. 1 bag of 50 kg cement is 1.25 cubic feet.

Concrete

Footing 

Volume = 0.70 x 0.70 x 0.25 x 25 numbers = 3.06 cubic meters

Dry Volume = 1.96 x 1.54 = 4.72 cubic meters

This 1.54 factor is given by the textbook. You can have tests to derive your factor.

Using the 1 : 2 1/2 : 5 ratio for 3000 psi:

1 + 2.5 + 5 = 8.5

Cement

4.72  x   1   =  0.56 cubic meters x  3.281^3  =  19.61  ~  25 bags of 40 kg cement

 8.5  

Sand

4.72  x   2.5   =  1.39 ~ 2.00 cubic meters

 8.5  

Gravel

4.72  x   5   =  2.78 ~ 4.00 cubic meters

 8.5  

Fieldwork No. 12

Good Morning Class. Today i am gonna teach you how to get organized with your calculations and estimates. I draw a straight line that separates the prime numbers and the two decimal places. To check your work put this on the MS Excel spreadsheet.

I usually start my design at the Roof Slab or the Suspended Slab. It behaves like a beam that you can treat it as one. The Shear and Moment Diagram shows that the force moves from bottom to top to down. 

For small houses you can design using graphs and tables but for more complicated designs you need further analysis.

As you can see in the diagram at the beams the maximum shear moves down up down so we splice top bars at the supports (L/4) while at the bottom bars we splice at midspan (L/2). 

At the columns you derive the loads from the beams, slabs and the occupancy loading provided by the National Structural Code of the Philippines (NSCP). We design the columns mainly in compression and buckling thus the slenderness ratio.

I provided 200 x 150 lintel beams for the opening at doors and windows.

We have poured the lean concrete at the footing yesterday so today we transfer the footing dimensions using the plumb bob.

Fieldwork No. 13

Good Morning Class. Today we transfer the footing dimensions down to the lean concrete of the trenches. We need at least 3 skilled workers here - one to hold the plumb bob, two workers below to pencil the coordinates. The carpenter holds the nylon string where the two nylon strings meet. Below the carpenter guides the plumb bob as near as the lean concrete surface but not touching it. When the plumb bob stops moving, the carpenter calls for the carpenter above if the nylon string is still correct. If okay mark the point with a pencil. Do this for all four corners. Using the chalkline (pitik) connect the four points. Do the same for the rest of the footings.

Check the fabrication of steel bars baskets 25 numbers. Measure the number of bars and spacing. The basket should not move. Instruct the carpenter to fabricate form works. Form lumber is used to mold the wet concrete into desired shape. The footing thickness is 0.25m or more or less 10 inches. We will install the steel bars and formworks on Monday because we need to fabricate the column main bars and tie it to the footing steel bar baskets.

Fieldwork No. 14

Good Morning Class. I've given the bar cutting/bending schedule for the column main bars 12mm dia while the stirrups are 10mm dia. I hired another Steelman to install the steel bars. The Carpenters work on the form works of the footing. The marked lines would still be visible but you can refresh the lines by the chalklines (pitik) or to those erased you re-establish the points using the plumb bob.  

As you can see in the diagrams the anchor of the column main bar rests on the footing basket. You make the basket by tying tie wires to make it immovable. The steel basket rests on the spacing blocks that we casted 25, 50, 75mm. The 75mm spacing blocks rest on the lean concrete. 

The foot of the column main bars are positioned diagonally. When the form works are installed the crew installs the column main bars and the stirrups and then fixed into position using our nylon strings and the verticality of the main bars using the plumb bob or better the theodolite. Calculate the distance of the edge of the column main bar to the Grid Line. Note the 50mm concrete cover on concrete structures under the ground.    

The vertical main bars will be supported by steel bars and good lumber to avoid swaying. 

Fieldwork No. 15

Good Morning Class. Here are our structural details. The anchor of the column main bar rests on the footing basket. You make the basket by tying tie wires to make it immovable. The steel basket rests on the spacing blocks that we casted 25, 50, 75mm. The 75mm spacing blocks rest on the lean concrete. 

Fabricating your form work is one investment you can make. In our case I will use 3/4" x 4' x 8' Hardiflex boards so we can use our formwork many times and its surface has a film that makes it somewhat waterproof and good moulding.

Thus I will order 7 Hardiflex boards for the 5 columns and will be re-used at the rest of the columns and beams. The Carpenter will cut it length wise and later on braced with good lumber.  

This is one set of formwork for the column as they cover the four sides. The braces will be connected by bolts and nuts. I prefer this system than using nails and screws so the bearing of the formwork will not be as disturbed after we have aligned its coordinates and verticality. Other formwork systems are the steel formworks which are plywood panels on steel frames. For bracing we can also the use of pipes and c-clamps, H-frames, A-frames, U-jacks and adjustable jacks.

While one Steelman and one Carpenter fabricate, the crew installs the steel bars at the footing. We pour concrete on the footings tomorrow.

Make sure the thickness of the footing is at least 250mm.