In this chapter we will present few live cases of damaged concrete structures which require a serial of repair and strengthening procedures these structures includes residential building, hotels and bridges and it have different levels of damages varies between major and minor damages.
Figure5- 1 Building that need’s repair
5.1. Repair of residential building
Three storing residential building located in New Cairo district, the building is still under-construction, it is still in the skeleton form.
5.1.2. Material used
The material used are; cement of high compressive strength (higher than the one previously used in construction) and reinforcing steel bars.
5.1.3. Project scope
In this building damages are detected after the removal of the wooden forms the damage was presented as (figure2, 3, and 4)
22.214.171.124Causes of repair
Figure5- 2 longitudinal crack Figure5- 3 spalling of concrete covers
And appear of RFT
Figure5- 4 longitudinal crack due to construction and structural defects
Figure5- 5 Figure5- 6
Buckling of column due to high compressive forces
Splitting cracks due to buckling of column
126.96.36.199. Repair of column by using (concrete jacket)
1. The slab is lifted up by wooden sections to remove the load from column
Figure5- 7 First step lifting up the slab with wood to be able to remove concrete cover
2. Cover is removed and steel bars have been inserted into old slab by epoxy to welded the new additional RFT to it (fig5-7)
Figure5- 8 Bonded steel bars
3. Creating voids in the slab to insert new RFT of the column into the slab to increase the bond between the columns and to make the process of purring concrete into shutter easier.
Figure5- 9 Breaking the slab to insert new RFT into it
4. After cleaning the surface insert new additional RFT and additional stirrups that preferred to be box stirrup to increase the bond then make the new shutter of the column from one or more sides according to repair design then pure the new concrete into column jacket.
Figure5- 10 Concrete jacket from one or more sides
Figure5- 11 Increase in the section dimensions of column after repair
188.8.131.52. Strengthening of the first slab using section enlargement
Some elements were not in need to repair such as first floor it has small deflection that’s not critical; we insert new top RFT then cover it with a layer of concrete.
Figure5- 12 slab of first floor before and after adding additional top RFT
184.108.40.206. Reconstruction of the second and third floor slabs
1. Lift up the repaired slab by wooden sections to avoid slab collapse.
Figure5- 13 Slab lifted by wooden sections
2. Remove base concrete and prepare the connection between slabs and columns
Figure5- 14 Removing old concrete
3. Make sure of Cleaning RFT from old concrete and ducts of electric wires.
Figure5- 15 Clean the main RFT of embedded beam from concrete
4. Build up the new shutter of the slab in the same level of floor then insert electric ducts
Figure5- 16 Wooden forms from in and out sides
5. Pour concrete into shutter then remove wooden forms after harden of reinforced concrete.
Figure5- 18 Curing surface of new concrete slab
5.2. Repair of Hotel Concrete Balcony Columns
Concrete can crack and experience vertical stress under the most unexpected circumstances affecting the structural building integrity and requiring immediate repair. When these situations occur in buildings used by the public, such as restaurants and hotels, repairs must be aesthetically pleasing and not raise public concern related to the buildings safety. In this case, concrete columns were pulling away from the balconies.
Grande Shores Ocean Resort, Myrtle Beach, South Carolina this is a 7-story resort hotel on the Atlantic beachfront. It is constructed using standard concrete skeleton method.
5.2.2. Material Used
Pre-cured Pre-preg w/peel-ply column wrap vacuum laminated; Designed by layout of job scope; Laminated with (#4020) Epoxy.
5.2.3. Project Scope
Concrete columns façade were pulling away from the balconies. Challenge was to strap and reinforce columns, yet make reinforcement aesthetically pleasing.
Figure5 -19 Repair of hotel column
Pre-preg column wraps allowed for fast installation, completing project with minimal disruption and prior to hotels busy season. With this method they were still able to function with only a small area of rooms closed off to public
Original design was to install 200 lb steel plates that would have added significant weight, would not have been aesthetically pleasing and would have closed a large area of the hotel losing them revenue.
Figure 5- 20 side view of concrete balcony columns
Figure5- 21 Elevation of concrete balcony columns
5.3. Highway-Bridge, Support Column Repair
Concrete bridge columns are an integral part of the integrity of highway bridges that may be damaged by various physical forces including earthquakes and vehicle accidents. Vertical effects on these bridge columns lead to significant variations in axial force demand which can result in fluctuations in moment demands at the face of the bent cap, amplification of moment demands at the girder mid-span, and changes to moment and shear capacity of the column.
In this case, concrete columns were deemed to be fatigued due to deterioration of steel reinforcement.
5.3.1. Material Used
Fortec 600 gsm unidirectional carbon fiber fabric w/ #4550 Epoxy Saturant and (#590) Epoxy paste.
5.3.2. Project Scope
Concrete Columns were deemed to be fatigued due to deterioration of steel reinforcement. Repair was to wrap columns using 600 gsm carbon fiber wrap utilizing onsite impregnator of epoxy saturate.
Figure5- 22 Wrapping column with FRP sheets
Wrapping column with Fortec carbon fiber fabric allowed for minimal road closure as would have been needed with old method of teardown and replacement of column. The #4550 epoxy allowed contractor to cure out in field under difficult weather conditions. With highs in the 60’s and lows dipping into the 40’s a night curing was a challenge.
Chapter 50live cases