Compiled Monthly Reports - AAiT CIVIL · PDF fileInternship2004 Compiled Monthly Reports 1 ... composed of beam supported one-way & two - way slabs [i.e. ground floor slab] ... [EBCS-1995]

Internship2004 Compiled Monthly Reports

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Introduction This booklet is a compiled, short-term report on internship practice for the four months of the overall internship semester. It covers the time duration from official commencing day of this

year’s{2004EC} internship program i.e. October24,2011 to the termination day i.e. February 10, 2012 during which time I’ve been part of different activities on five different sites. As a result, the report format includes

Site description: functional use of the building & the structure’s general profile.

Status upon my first encounter: status of the project when I first arrived.

Project progress: major tasks undertaken in my presence as part of the project.

My part in the activities: what I specifically contributed to the progress of the project. My hosting company is Woder General Contractor. The company is a class4 construction company on the verge of transforming into Class2 by meeting the requirements in the near future.

It was founded by two charismatic and zealous individuals with a lot of commitment, Ato Wondesson Bekele & Ato Dereje.

The company has undertaken & is undertaking a number of tremendous projects quite satisfactorily. The G+17 hotel project near Tewodros Stadium in Bahir Dar is one good example. On my first day at the company, Ato Wondesson, Managing director & co-owner of the company, briefed my colleagues & I on the company’s background & sector of activity ongoing projects at hand workflow in the company what we should set out to achieve.


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Month1: October24, 2011 - November18, 2011 GC

Site1: 2B+ G+ 2 Residential house near Carl

square Architecturally eye catching, residential, fancy house with a kidney shaped pool in the basement, a helical staircase which encloses a panoramic lift & a ground floor slab which is open down to the pool {5m diameter circular

opening} From structural point of view, the building is composed of beam supported one-way & two-way slabs [i.e. ground floor slab] and 260mm flat slab [first & second floor slabs]. The beam & column arrangement & spacing are not somehow ‘conventional’ in the very

essence of the word. This is due to the intended architectural appearance. The 8m column spacing supporting the 3m projecting cantilever which acts as a shade for the pool is one example.

Picture1 Model of site1 building

When I first arrived there, false works, panels & supporting scaffoldings were being put in place for second floor construction.

Tasks undertaken after my arrival include

second floor reinforcement laying out & casting

provision of sanitary & electrical system pipes for second floor slab

setting out & construction of shear walls

construction of helical & two-flight staircases

water proofing works for the basement shear wall

plastering works My specific contribution includes

1. Overlooking second floor slab reinforcement layout The second floor is a 260mm thick flat slab with a lot of reinforcements uncommon in residential houses. Since the whole floor has curved peripheries & in some cases openings, the bar schedule dictates the use of variable length for a single bar type. So I proportioned the lengths based on the available area for each & every bar types of top & bottom reinforcements on both major & minor axes. During this time, a great care was taken to the overlapping positions. For bottom reinforcements,

overlapping was provided near the supports while for the top ones it was provided on spans. As a matter of fact, quiet a large number of the rebars tend to fall in the length range of 10-12m. So the potentially wasted portions of bars were left as they are {i.e. @12m} coz cutting them out or not does NOT do any good to anyone rather we anticipated their presence is better. Also an extensive structural drawing cross-checking & revision was carried out which surfaced out -same span assigned to two or more than two spacings

-omitted negative bars by the designer


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As a result, more of conservative remedial measures were taken. - the better of the spacings were implemented - the omitted bars were reported to the site engineer & through the common procedure they were eventually provided.

There were also some discrepancies between architectural drawings (floor plans) and structural drawings. -omitted part of slab near the major helical stair case {architectural requirement}

>>> minimum reinforcement (ɸ10 c/c 30cm) were provided since no load is expected on that part of the slab - position of false columns emerging from the slab >>>the roof truss supporting top tied beams were supposed rest on a number of columns that do not

continue down. Their locations indicated on architectural plan & structural beam lay out plan show discrepancies. So I anticipated punching shear might be eminent since the structural analysis & design outcome shows one thing & we were about to construct another thing. As a result, the structural engineer was called up on and provided the correct positions. Bar dimension alteration {due to unavailability} was a rampant activity I was always involved throughout the project.

2. Stair case construction A. External, partially curved stair case On site design revision was a must because -basement headroom distance was changed [from 4m to 3.91m] so as to construct the main circular staircase [it was not feasible as per the original design] -the one flight stair case was NOT ideal for vertical transportation [too many risers] So I proposed an intermediate landing at a height of 1.96m making the stair case a two way flight. Consequently, - The riser-thread arrangement was revised / redesigned {architecturally speaking} - The plan was transferred onto the real world {maintaining structural integrity with the whole structure specifically with ground floor slab}

- Two alternatives of supporting system for the stair case were proposed

extended grade beam from a nearby column{by welding}

masonry supporting footing Finally, the second alternative was put into effect. A new reinforcement provision was then requested from the designer. {PS All this activity was documented in the site book}

B. Ground-Basement helical staircase >Architectural design revision {to meet the actual site condition & construction progress} >Setting out of the helical staircase -by the principle of simple offsetting 3. Shear wall construction

The primary purpose of the shear wall was its aesthetic value. It somehow augments the grace of the whole structure. It has its own footing and is in intact connection with the major skeleton. This was achieved by extending the reinforcements in to second floor slab with an overlap length of 1.5m and casting them monolithically. Since the one critical shortcoming of flat slab is its susceptibility to lateral instability, the shear wall attributes a great deal of intactness to the structure to check any unforeseen lateral shocks.


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This is particularly a very advantageous input since international building codes classify Addis Ababa as one of the seismic prone regions in the country. [Design Ground Acceleration= 0.3g] PS. The seismic hazard map of Ethiopia [EBCS-1995] dictates Addis Ababa as low seismicity region with design ground acceleration less than 0.05g {Zone2}.

Setting out of the shear wall pad was done by simple offsetting from the nearby column on axis1. The pad was set out by offsetting from the nearby two columns as the architectural plan dictates. The formwork was then prepared, lean concrete produced and placed, reinforcements put in to position, and then casted.

Fig.1 Front Elevation of site1 structure

Site2: 2B+ G+ 12 Mixed use building around

‘Sar Bet’ This site was one of the many projects that the

supervising engineer of site1 was responsible for. Thus on this specific project, I was on the consultant side. The condition was a very ideal one since both sites 1 & 2 were not far apart and I get to play on both sides of the sector i.e.

consultant & contractor. The building was initially designed to have a sharp arc face on one side. But due to side road standard upgrade, a certain amount of area was trimmed. So the whole architectural design on that periphery was redesigned to incorporate the new amendment.

Picture2 The ribbed mat foundation on site2


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The structure is composed of edge supported one-way & two-way slabs with an opening extending all the way to the top skylight.

The basement is intended for parking.

Soil investigation was majorly based on zonal soil map which dictates more or less the same soil for the region between Pushkin sq. & Mexico sq. But few borehole investigations were also taken. The results of the investigation & the actual excavation work revealed the presence of a very hard stratum of rocks. So the second basement was no more an ideal option due to the high cost excavation. Once again the design was revised.

The footing is a composite foundation comprising of grid mat & a single isolated footing only to support the long span beam underlying the basement floor slab. The grid mat has 40cm deep solid part & 70*130cm grid beam with 4 legged stirrups.

When I first arrived there, pre-foundation works were already on progress. These include site clearing, excavation and footing & column grid setting out. Lean concrete & footing reinforcements were also in place.

My specific contribution was somehow limited to observations & assisting the supervising engineer in some quality control tests.

-aggregate quality by visual inspection [red ash presence was highly undesirable on the footing work] -sand quality [silt content test by density bottle method <6% was ok// 6-10% was essentially washed before use // >10% was automatically rejected] Some peculiar features of the site include

1. Volume batching by cart not by box The usual practice in batching by volume is the use of standard boxes; 16*40*50 cm3 or 18*40*50 cm3 for one bag of cement for C-30 & C-25 grade concrete respectively. But on this site, carts were used instead of standard boxes. 2. Use of epoxy grout to continue work on previously casted concrete work.

{Epoxy grout consists of epoxy resin, epoxy hardener and sand/aggregates. Though epoxy grout appears to imply the presence of cement material by its name, it does not contain any cement at all. On the other hand, epoxy hardener serves to initiate the hardening process of epoxy grout. It is commonly used for repairing hairline cracks and cavities in concrete structures and can be adopted as primer or bonding agent.} Despite this fact, the use of epoxy grout affects bonding performance of bars to concrete.

The bonding of galvanized bars to concrete is lower in early age owing to hydrogen release when zinc reacts with calcium hydroxide in concrete and the presence of hydrogen tend to reduce the bond strength between galvanized bars and concrete. However, bonding will increase with time until the full bond strength of ungalvanized bars is attained.


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3. A little bit unorthodox contractual arrangement The structure is being erected by a Chinese contractor who rented the permit certificate of a local contractor. As a result, the site engineer, the foreman & the mix designer are all Chinese. There are also a couple of Chinese bar benders & carpenters.

This feature created a language barrier. Also the client was raw material provider which allowed him to directly intervene in the day to day progress of the project. As a result, confrontations between the client & the supervising engineer were part of any day of the week. One specific argument was however brutal as it changed everything. Foundation columns were about to be casted. The client provided Pozzolana Portland Cement (PPC) which he bought in the summer time while cement price was quite high. It was also on the verge of expiring. But the

engineer refused to use the cement coz the structural design strictly dictates to use C-35 grade concrete produced with Ordinary Portland Cement (OPC). This made the client to lose about 150,000ETB by selling the cement for the current price and the engineer to quit the site. One important thing I get accustomed to working on this site is a site book. It’s a book where all the major tasks undertaken in a day are written. It is then signed by the supervising engineer and the

contractor’s seal is stamped. It’s the primary source of information if, GOD forbids, some kind of failure or defect occurs.


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Month2: November21, 2011-December16, 2011 GC

Site3: B + G+14 Mixed use building in front of

‘Buna ena Shay’ The building has already become one of the land marks of the area, a monumental figure to the neighborhood. It is already on finishing stage.

Picture3 G+14 building contemporary

stage

During my time there, I was part of the following tasks. 1. Surveying work - Two-way slope setting out

Since the building on the edge of a block parcel, it is bound by two streets. And the outside area was intended for car parking. Thus to check any prevailing flooding and also to harmonize the area with road, a proper & uniform amount of slope was needed on both sides. -Taking the road as zero level reference point, back s ight & fore sight readings were taken from the top of the bottom stair. -Horizontal distance was also measured.

-The slope was then calculated by

𝑠𝑙𝑜𝑝𝑒 =𝑉𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒

𝐻𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

Since there was an obstruction [a fence] between the building & the road, the parking lot was temporarily to be built up to the fence only. Thus the vertical height that needed to be attained at the fence was calculated as

𝐻𝑒𝑖𝑔𝑕𝑡 = 𝑠𝑙𝑜𝑝𝑒 ∗ 𝑕𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 Then it was marked and a rope was tied from the stair to the fence and hardcore & reinforcements were placed. 2. Concrete pavement construction

15cm hard core + ɸ10 mesh with non-uniform spacing + 15cm concrete cover = conc. pavement

The 15cm thick hard core will provide a uniform support for the slab. The flexural strength of

the concrete pavement is derived from the ɸ10 c/c 30cm mesh. The 15 cm concrete cover

provides a smooth & reasonably skid resistant surface.

Expansion joints were also introduced. 3. Finishing works I was able to witness aluminum framework & fiber glass provision works.


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Site1 2B + G + 2 Residential Building near Karl Square

[Refer Report1 for Site Description]

Tasks undertaken this month include

backfilling & compaction works in the garage & the basement

construction of the garage with its own footing

water proofing works for the basement shear wall

construction of masonry retaining wall in the basement

construction of basement floor slab

plastering works My specific contributions include 1. Retaining wall construction Retaining wall that embrace the pool was constructed because the space below the grade beam was supposed to be filled by a good quality backfill but the owner requested contractor to make use of the

space instead of filling it. So the design was once again revised to incorporate the new "under-basement" rooms. Meanwhile, the natural soil level still needed a supporting mechanism so a stone masonry fence and retaining wall bedded in cement mortar of mix ratio 1:4 was built. Also 50mm thick lean concrete in C-5 with minimum cement content of 150kg/m3 was placed under the stone masonry fence and retaining wall. 2. Water proofing works on front shear wall Two coats of hot bituminous water proofing were applied on the retaining wall and plastered concrete wall around the building by using brush. Also 10cm thick solid concrete block wall bedded in cement mortar mix 1:4 over damp proofing material was built on the front shear wall. 3. Takeoff sheet for reinforcement

Upon the completion of 2nd floor slab reinforcement layout, I was fully entitled to prepare the take off sheet of reinforcement. This task was as much sensitive as the structural works

coz it has grave final effect on one of the most important issues of both the contractor & the

client i.e. cost. 4. Construction of basement floor slab The original plan dictates -100mm thick RC slab, -250mm thick hard core, -800mm selected fill.

But since a second basement was a new reinforcement was formulated and put into effect.


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Month3: December19, 2011–January13, 2012 GC

Site4 2B + G + 12 Mixed Use

Building near Bole

Medhaniealem This under construction asset is the property of San Bird Real Estate.

It has curved periphery on the near side of the major road and all the way to the top. Its composed of edge supported solid slabs [basement & ground floor slabs] and 300mm thick ribbed slab with submerged beam [1st to 12th floor]. The plastering & finishing works are so delicate that the slabs appear to look like flat slabs at first glance. The ribbed slab is made of C-

25 60mm thick concrete slab 80x240mm one way RC ribs with c/c spacing of 400mm and200x400mm hollow concrete ribbed blocks and concrete girder.

Fig.2 Floor plan of the building[ 8th – 10th ]

When I first arrived there, preparations were being undertaken for 7th floor construction. These included erecting of false work, placing of panels and extending of the transporting lift. I-section false work & metal scaffolding were being used since most of the construction area is fairly rectangular unlike Site1 [Karl Square] where the contractor had to use wood false work & props due to the prevalent irregularities of the slabs.

Tasks done after my arrival include

Reinforcement lay out & casting of 7-9 floors and associated columns

Curing works

Construction of elevator shear wall

Construction of stair cases

My specific contribution was in the areas of 1. Provision of rebar, HCB lay out and casting

The ribbed slab structural drawing dictates 60mm thick concrete slab 80x240mm one way RC ribs with c/c spacing of 400mm and200x400mm hollow concrete ribbed blocks and concrete girder. Also there were a few hollow parts here & there. As a result, integral beams came into the picture to account for the area of steel {As} lost to the holes.


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2. Curing works The columns were being cured by means of ponding with poly propylene sheets (sack).

Peculiar features of the site are Very rapid ease of construction owing to surplus availability of formworks, scaffoldings &

false works. Very high ground water level which almost submerged the two basements.


[Refer Report1 for Site Description]

This month a very unfortunate event took place on this site. Failure happened on the first floor slab and thus everything came to a halt. The second floor slab was being casted zone by zone. A little after the 3m extending cantilever was casted, an unusual, profound sound came from the first floor slab and then props started to bend & shoot in to the air with high velocity. It was a very stupefying moment on my part. What was done? Props were put in place to support the second floor slab cantilever so as to relieve the first floor

cantilever from the unaccounted construction load.


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Month4: January13, 2012 - February10, 2012 GC

Site5 G + 8 Mixed Use Building near British

Embassy, Gurd Sholla The client on this commencing project is Dr. Emebet, a decorated dentist nowadays. The building has somehow a classic external appearance owing to the intended finishing to be used. Fine external wall finish plastering

along with artistic troweling and parapets is to be used unlike the prevailing practice i.e. provision of aluminium cladding with fiber glass. It has isolated footings all in all. The rocky nature of the area is one of the contributing factors for this selection. The floor slabs are

edge supported two-way slabs.

Plate11 Status of site5 up on my arrival

As of my arrival, I was there from the very first day.

Tasks undertaken during my stay include

Site surveying Site clearing Bulk excavation marking Bulk excavation Excavation depth control by surveying

My specific contribution include

1. Preliminary surveying This was done in order to determine the slope of the site and pin point heights from asphalt road [i.e. NGL in this case]. As a result, back sight readings from the NGL and foresight readings from selected points in the site with a gap of 3m were taken. The heights of these points relative to the NGL were determined.

ElP= ElNGL + BS - FS The slope was then determined by simple arithmetic calculation. 2. Bulk excavation Marking Due to the current company resource allocation paradigm, the overall excavation & transportation task was subcontracted to an external party i.e. load and cart away of surplus excavated material to a suitable damping area allowed by the municipality not more than 10km from the site.

It was our duty to provide them with the working inputs. So the depth of excavation for reasonably spaced points in the site (3m) was calculated and marked with ink on the respective points. This was done by taking in to account that all earthen materials are to be removed to a depth of 1m from the NGL. Excavation for foundation footing in rocky soil to a depth exceeding 150cm but not exceeding 300 cm from natural ground level is also to take place shortly.


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3. Excavation control by surveying Excavation and transportation is one of the many crucial factors that attribute to the cost of a certain project. So, grave attention is given to this finance-sensitive task. The subcontractor’s work was checked & rechecked by us.

A certain convenient premarked point on either side of the demarcation fences is taken as a reference and its height is marked. Its parallel equivalent (on the same axis at the same depth from NGL) on the other side is determined using level. The two points are linked by rope and the excavation depth on 1m intervals is checked using a plum bob and a tape whether it is adequate or still needs excavation.


[Refer Report1 for Site Description] This month remedial measures were being drafted for the unfortunate failure. These include

Structural load bearing wall rising from the basement all the way up to second floor slab

Jacketing using epoxy

Recasting with more shear reinforcement provisions [column capital]

Documents

Compiled Monthly Reports - AAiT CIVIL · PDF fileInternship2004 Compiled Monthly Reports 1 ... composed of beam supported one-way & two - way slabs [i.e. ground floor slab] ... [EBCS-1995]