In: Civil Engineering
You are a Structural Engineer working in a structural repair and rehabilitation consulting firm. You have been assigned to provide the answers and solutions for the following job: “Some cracks were observed on a suspended reinforced concrete slab on an existing public building. As these cracks raised public concerns, the owner has decided to carry out a structural investigation into the cause of cracking to check the structural integrity and determine the remedial works to be done.” (a) Outline and explain the process of investigation that would be recommended to identify the causes of the cracks.
(b) State Four (4) possible causes of the cracks?
(c) Propose Three (3) suitable tests to estimate the in-situ concrete strength.
(d) From the investigation, it was found that the cracks are due to structural overloading. Recommend a method to strengthen the existing slab and suggest a method to repair the crack.
Answers
A) step 1: Discuss with client or owner if building basic questions
about when was building constructed, ask for building drawing or
detail drawing If possible and followed by ask when was 1st crack
appeared and also ask about concrete failing deflection, large
crack, water leakage.
Step2: Visit site along with drawings of respective bldg, check
whether bldg construction were as per drawings, check whether there
is change in structure match it with drawings, capture photo and
give date to that and Mark the width of crack it shouldn't be more
than .3mm, check all other possible cause such as tilting of any
structural member, deflection leakages, corrosion.
Step3: Understand cracks and it's cause, find type of crack it is
live or dead etc.
B) Causes
1.Crack may be temperature variation
2.Permeability of concrete
3.Corrosion of reinforcement
4.Poor structural design
5.Creep
6.Shrinkage
7.Moisture variation footing movement, etc.
C) Suitable test would be
1.Rebound hammer test,
2.Ultrasonic pulse velocity and
3.Pullout test
D) Methods for strengthening and crack filling
1.Epoxy injection
2.Gravity filling,
3.Grouting and sealing,
4.Stitching ,etc