Pictures....grrrhhh!, wish the copy and paste was possible....
PS/the only reason we're talking about this is because landslides can cause loss of life and damage to property of the human.
And when they go off, they are like huge unstoppable monsters that dont give precise warning signs of their arrival.
However, when you see animals and birds darting off days earlier, the warning signs are good enough.
Bringing you up to speed!
First, see how devastating a land slide can be.
http://sorisomail.com/email/42722/ja-viram-desmoronar-uma-montanha.html
Sometimes it can be so obvious, Kampala city surburb, Uganda (the author calling it 'catastrophe in waiting')
http://www.monitor.co.ug/News/National/-/688334/896256/-/view/printVersion/-/xfo1yv/-/index.html
Also this one.
land slide manner
And this one below actually caused serious loss of precious life in Bududa, Uganda. Bududa(March 2010)
http://www.nation.co.ke/News/africa/-/1066/871740/-/122ljwsz/-/index.html
Residents of Bududa look at what remained after the landslide that left 80 dead and 100 missing.
Now you've got the picture of what we are talking about.
The simplified concept of a land slide
A land slide is when the soil along and near the slope fails to sustain its own weight and the weight of objects(trees, vegetation, houses, vehicles) above it.
These weights bring about stresses in the soil. The concept is simple, when these stresses exceed the soil's cohesive ability then the soils break up along made up slope lines causing a land slide. The soil's cohesive ability is in simple terms its strength or its stability.
These slope lines are called slip planes.
In such a case, the slope is said to be unstable....an unstable slope.
Do not ask the engineer to precisely predict slip planes, soils can have many inherent little fracture planes.
The most unpredictable engineering materials is soil.
clay landslide morphology land slide effigy
Categorising slopes
We do have built-slopes and natural slopes.
Built slopes are normally found around homes, business premises and factories.
The figure below is a styled up built-slope good for a home/business area.
Built-slopes are what we commonly we refer to as retaining walls.
Natural slopes are those around villages, country homes and roads, schools factories but also on hills or mountainous areas.
Image credit: http://farm1.static.flickr.com/3/3295992_af658c0623_o.jpg http://www.leo.lehigh.edu/projects/seismic/pictures/6.jpg land slide mannerism
land slide form
Moving around Kampala-Uganda, the potential for land slides is just way to much. And the most areas I have seen are in residential zones for those putting up homes on hills. The situation is almost unlike other cities in other countries. Kampala is hilly throughout, that's one of its unique features. Some of us have on various occasions been asked to propose solutions for these steep slopes and the methods we've proposed have been called expensive as they get to a tune of about 15% of the construction of a home. In money terms, that's about 10m Ushs(5,000$) for ordinary homes(three bedroomed). And this value can go up to over 100m Ushs (50,000$) for bigger homes and organisations.
Likewise unprotected deep excavations for storied buildings within Kampala are still going on despite the recent soil collapses killing people. And the Ugandan engineering community (UIPE) has already talked about it but it has not sunk in well into the mainstream life.
This is where you, the information distributors, come in. And the way forward is simple. Big-styled buildings needing deep excavations will require that the contractors present construction methods to the consultant and then to the council including details designs/drawings of how to protect/brace these steep slopes arising from deep excavations...but that's for another day. Key issue is, this is a man-made slope that can easily fail causing life-loss to construction workers. And by the way, similarly around the world...however, the HSE(health, safety, environment) institutions in some countries, say, scotland, have some strength...case in point, a contractor last month was persecuted for failing to support a 1.8m excavation within the given deadline, click the link...link 1, link 2
piles
Cause of unstability in existing or made slopes
Three main causes that have to be curbed are
1. The human
2. Water,
3 Earthquakes/tremors
The biggest cause of instability for existing slopes is water. All water has to be directed.
Water has a tripple effect on soils.
1. It reduces the soil's cohesive strength
2. It adds its own weight to the soil.
3. It adds pore-water pressure within the soil.
Earthquakes enhance slip planes or create new ones and likewise reduce soil stability through direct tug&pull.
Looking from the engineering viewpoint, the human is also a menace when it makes deep excavations and many judgmental errors. The human has to be curbed through awareness because unlike the other two, it has a mind and can WILL...but if stubborn, then the law is needed when the problem is community-affecting or letting it be a victim of its own fate if it(this human) ridicules all your efforts to help it.
Most of land slides occur during unending rainy seasons and strongly increased by tremors and built-up environments, such as paved yards, roads and most especially roof tops. A strong down pour is not as harmful but those unending soft-pouring rains are.
Whenever it rains, the cohesive ability in soils is reduced. The more it rains the more the reduction in cohesion.
This is because water infiltrates within the soils through the soil pores making it waterlogged.
In otherwords, the more waterlogged the soils, the more its weakness in strength.
If your house is situated near a slope, never give chance for the slope to ever become waterlogged by choice.
This water has to be drained out as fast as possible.
That's why most people put up hidden drains or weep holes(see figure below) along built slopes or retaining walls (see figure below).
http://www.burkesbackyard.com.au/img/archive/1814/retainingwall_22.gif
Built slopes without weep-holes WILL fail.
When you move around, you will see constructors including weep holes on retaining structures.
Slopes rarely fail on their own weight, and most especially for soils in Uganda.
Are people aware?
I honestly do not know if you look at the picture below.
PHOTO BY ISMAIL KEZAALA. from www.monitor.co.ug.
Taming Land slides
So this is where the engineer's assessment, design and mode of construction comes in.
The engineer does not work alone...for community projects and beyond, a full complete team is needed. Briefly outlined below
1. Site Investigation(investors, construction consultants, economists, politicians, enviromentalists, geologists,... list goes on as needed)
Construction consultants here include architects, engineers, hydrologist and surveyors
2. Benefit (investors, economists, politicians, enviromentalists,.. list goes on as needed)
3. Planners(consultants...)
4. Soil properties (geologist)
5. Models & Simulations(consultants)
6. Hazard rating and mapping (consultants, council)
7. Risk and cost analysis (consultants, economist)
8. Finalised engineering design&details.(consultants)
9. Construction.(consultants, builder)
When the soils are highly cohesive, you do little on steep slopes, less expensive.
When the soils are less cohesive, you're advised to make the slopes less steep or built-up properly.
Key factors.
1. Stay away from slopes.
2. But if you cant contain (1), then stay at a distance from the slope equal to its height.
3. Do not reside at the foot of a slope, be above it and at a distance away from the slope equivalent to its depth.
4. If you cant contain (3) & (1), and are that upclose to the slope, build an engineered retaining wall and for God's sake provide drainage options for stormwater esp. that off your roof.
You can turn a nuisance steep slope into an architecturally looking beautiful retaining walls around your homes.
All you have to do is ask the architect for beauty and the engineer for structural feasibility and other stakeholders for related feasibility(s).
That second pic is a honey combed wall. Common if you walk around.
Designs exist, freely given if needed.
5. Also do not forget that for big slopes, needed are anchor rods or dowels (figure below) + chainlink(or strong wire mesh or geosynthetics, see figure below) along the slope + lime-stabilised soils + and proper drainage of stormwater channels.
rock slope stabilization Vegetated steep slope application photo
http://www.terrafixgeo.com/uploads/60_SierraScape_7M.jpg
6. With inclusion of some concepts in item 5, you can beautify your retaining wall with a serious stone facading.
Retaining walls and vegetated steep slopes - system drawings
Retaining wall application photo
6. Soil stabilisation(see below) also somehow tames land slides as seen in the deep hills of Kigezi, Uganda.
okay.
Nathaniel. Ddumba
MSc. Str.Eng, BSc.Civ.Eng.
M'IABSE, M'UIPE, M'SEAINT.
Wednesday, July 21, 2010
Saturday, March 6, 2010
written in a hurry
[unedited]:
| n'joy |
WHEN ENGINEER IS ACCUSED
~~~~~~~~~~~~~~~~~~~~~~~~
Here is one engineer last year in Uk who got into a contract to supervise a certain job and got into serious trouble. It was the contractor who had put the engineer in the mess and the client latched onto the engineer to pay for the errors because he was not on site when the contractor was making the errors. Ofcourse, the engineer could win the court case but the time and money to do all this was getting on his nerves plus the fact that he had other work on his plate that he wished not to be affected. Such was his weakness and he transferred it to the institution of structural engineers for solace. As I write now, he has probably done a few calculations and has probably accepted to take in the error, so that his works are not disturbed. Point is, how can the Institute of Structural Engineers in UK protect such and do they have a provision for such?
WHEN THE CLIENT ASKS FOR TOO MUCH!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
He asked, how much can such a roof truss cost?
The foreman said, about 75,000/-.
Ah!?, and 10trusses would cost 750,000/=?
No, said the foreman, but 300,000shs.
And that confused the client who wanted to know the exact price so that he doesnt
feel cheated by the foreman
The client wasnt convinced for he thought that in that case if
300,000/- is for 10trusses then for a single truss, that is 300,000/10 = 30,000.
"No sir", said the foreman, "it has to be atleast 70,000/=."
"You think I didnt study math?", said the furious client.
And the foreman humbly replied: sir I know you are one of these great
mathematicians but that is academics and this is our turf, in a real situation,
sir, making a single truss means a waste of my day's effort if you are to count
theoretically like that. Realistically, the whole day would be wasted.
Thus asking me to make one truss in a day is more expensive than making 10trusses.
And the client went to look for another foreman.
I only got to know when the client was narrating to me the whole ordeal
and I wondered how I would break the news to him, that you(the client) were the
wrong one instead.
This was one of the many times when clients prefer to handle the technicians
on their own. This is very problematic everywhere in the world you'd go to.
Nathaniel
feb'10
WHEN THE LABOUR PRICES GO UP
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Client: I want to pay you on a daily basis
Foreman: ok.
Client(C): so how much
Foreman(F): 95,000shs
C: (he is not amused):
F (notices it and explains): In a day, I would need two skilled ones and two porters
to do the building work.
Meaning that I get 50,000/=, every skilled man gets 20000/= and a porter gets 7500/=.
And the supervising engineer gets off 2000/= from my salary for sacred trust issues.
C: But last two year, I read that a foreman gets 35000, skilled=12000, porter=5000. You cheating?
Why the increase?
F: Because you have increased price of bread at your supermarket.
C: (not amused)
F: actually more sir, your transportation system was increased by 500/=, sugar increased by 300/=, food by 300/=, fruits by 400/=, you, the chairman of the board for our school increased the fees by 100,000/=.
In otherwords, sir, you've increased all the basic necessities, and that makes me unable to sustain my family unless when the salary increases by an extra dinaro!
C: ashamed, he now knew that "what goes around indeed comes around!"
He was wrong in thinking that those stinging decisions only affect the others minus him.
Little did he know that every decision he would make would eventually get back to him
through the interrelated network of activities that joins all people within the community.
He now embarked onto breaking this interrelated activities where the workers would be made to pay for more without the workers having sufficient reasons to ask for a wages increase! he dreamt on.
WHEN THE LABOURERS DID THE TRICK ON THE CLIENT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As the client figured out ways of making more money, he thought of a way of breaking the inter-related activities so that the construction worker pays more for the necessities without the workers asking for more during the construction of his new supermarkets.
Huh! he continued dreaming on. The workers likewise were figuring out of making more money from the client.
They had kind of made it easier on them.
They had persuaded the client to pay them on a daily basis.
Meaning that a wall that would be constructed in a single day would take 1.5days.
It is that easy, even when the client is on site. The workers would be so busy yet
not finishing the works in the required time. This extra trick by the workers was
due to the fact that the client had refused to increase their daily package meaning that
- the foreman would get 35000/-
- the skilled worker 13000/-
- the porter 6000/-
- the supervising engineer taken out of the picture.
The client was particularly so confused as to why the supervising engineer(also called architect) would visit the site anyway and more to that get double the money, part from the foreman and part from the client himself.
THE CLIENT'S CONFUSION OF THE SUPERVISING ENGINEER'S ROLE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Thus the client did the simple math.
Ideally, the supervisor would visit the site on mondays, wednesdays and saturday morning and would get
65,000/- from the client plus the sacred trust fee from the foreman.
So reasoned the client, sitting on his porch facing the lake waters. Pondered him that if the supervising engineer is taken out of the picture, him alone would save 65,000shs x3day=195000shs per week.
And this saved money would be used to buy an extra 1000bricks on site that would be able to build an extra 6m long wall on his supermarket.
Behold, the client had done his math up to this point and saw it was good. In order to fill the vacuum, he
did raised the level of the foreman to be a site engineer and according to him, all was good.
Problem was, he was breaking the sacred trust between the supervisor and the foreman who are the only ones
who can fully discuss technical issues in between them. Likewise, the lesser workers had seen it as an opportunity to pounce on any opportunity to trick the socalled witty client and the technician on material usage. The client has not any idea that these workers have a kind of psychology that sometimes surpasses a university-trained psychologist. These workers could would infiltrate the client's mind with such petty issues as to how they have built similar houses even without the need for those socalled professionals who call themselves architect, engineer, surveyor...etc! And the client had bought it just like so many clients do these days.
And thus the building started developing cracks. And the client recalled the supervisor telling him that it was your work to confirm that the drawings are correct. "THAT'S WHY I PAID YOU FOR THE DESIGN", shouted the Client.
WHEN LOCAL WORKERS'S PSYCHOLOGY RUIN THE CONSTRUCTION INDUSTRY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Who, for heavens sake would have believed that these people use their mind in the most cunning of ways?
Which later gets discovered by the general public?
WHEN THE LAZY ENGINEER GOES SELFISH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The client reasoned out the engineer by telling a story of a friend who suffered at the selfishness of the engineer. He thus concluded:
It wont take you long to notice that so many engineers step out of the loop of their fellow engineers trying to look for a little extra more buck and by so doing steping out of the code of ethics boundaries that every engineer has to follow. It wont take you long to see that such engineers have stagnated to the extent that what used to apply some years back is already taken out of the picture.
And the client had been warned.
The client had been told that when chosing an engineer, seek to know their activity roles with other fellow professionals, professional societies, for such constant activity roles makes two or more people grow within the profession.
The client had to listen.
THE MAKING OF A QUACK ENGINEER
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Come on guy, what have you been doing in the village?
I've been building huts and i have seen that they do not fall.
I have a lot of experience big enough to build a skycraper.
And the client was savvy not for anything but he saw this one
would be cheaper.
[unedited]:
| n'joy |
WHEN ENGINEER IS ACCUSED
~~~~~~~~~~~~~~~~~~~~~~~~
Here is one engineer last year in Uk who got into a contract to supervise a certain job and got into serious trouble. It was the contractor who had put the engineer in the mess and the client latched onto the engineer to pay for the errors because he was not on site when the contractor was making the errors. Ofcourse, the engineer could win the court case but the time and money to do all this was getting on his nerves plus the fact that he had other work on his plate that he wished not to be affected. Such was his weakness and he transferred it to the institution of structural engineers for solace. As I write now, he has probably done a few calculations and has probably accepted to take in the error, so that his works are not disturbed. Point is, how can the Institute of Structural Engineers in UK protect such and do they have a provision for such?
WHEN THE CLIENT ASKS FOR TOO MUCH!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
He asked, how much can such a roof truss cost?
The foreman said, about 75,000/-.
Ah!?, and 10trusses would cost 750,000/=?
No, said the foreman, but 300,000shs.
And that confused the client who wanted to know the exact price so that he doesnt
feel cheated by the foreman
The client wasnt convinced for he thought that in that case if
300,000/- is for 10trusses then for a single truss, that is 300,000/10 = 30,000.
"No sir", said the foreman, "it has to be atleast 70,000/=."
"You think I didnt study math?", said the furious client.
And the foreman humbly replied: sir I know you are one of these great
mathematicians but that is academics and this is our turf, in a real situation,
sir, making a single truss means a waste of my day's effort if you are to count
theoretically like that. Realistically, the whole day would be wasted.
Thus asking me to make one truss in a day is more expensive than making 10trusses.
And the client went to look for another foreman.
I only got to know when the client was narrating to me the whole ordeal
and I wondered how I would break the news to him, that you(the client) were the
wrong one instead.
This was one of the many times when clients prefer to handle the technicians
on their own. This is very problematic everywhere in the world you'd go to.
Nathaniel
feb'10
WHEN THE LABOUR PRICES GO UP
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Client: I want to pay you on a daily basis
Foreman: ok.
Client(C): so how much
Foreman(F): 95,000shs
C: (he is not amused):
F (notices it and explains): In a day, I would need two skilled ones and two porters
to do the building work.
Meaning that I get 50,000/=, every skilled man gets 20000/= and a porter gets 7500/=.
And the supervising engineer gets off 2000/= from my salary for sacred trust issues.
C: But last two year, I read that a foreman gets 35000, skilled=12000, porter=5000. You cheating?
Why the increase?
F: Because you have increased price of bread at your supermarket.
C: (not amused)
F: actually more sir, your transportation system was increased by 500/=, sugar increased by 300/=, food by 300/=, fruits by 400/=, you, the chairman of the board for our school increased the fees by 100,000/=.
In otherwords, sir, you've increased all the basic necessities, and that makes me unable to sustain my family unless when the salary increases by an extra dinaro!
C: ashamed, he now knew that "what goes around indeed comes around!"
He was wrong in thinking that those stinging decisions only affect the others minus him.
Little did he know that every decision he would make would eventually get back to him
through the interrelated network of activities that joins all people within the community.
He now embarked onto breaking this interrelated activities where the workers would be made to pay for more without the workers having sufficient reasons to ask for a wages increase! he dreamt on.
WHEN THE LABOURERS DID THE TRICK ON THE CLIENT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As the client figured out ways of making more money, he thought of a way of breaking the inter-related activities so that the construction worker pays more for the necessities without the workers asking for more during the construction of his new supermarkets.
Huh! he continued dreaming on. The workers likewise were figuring out of making more money from the client.
They had kind of made it easier on them.
They had persuaded the client to pay them on a daily basis.
Meaning that a wall that would be constructed in a single day would take 1.5days.
It is that easy, even when the client is on site. The workers would be so busy yet
not finishing the works in the required time. This extra trick by the workers was
due to the fact that the client had refused to increase their daily package meaning that
- the foreman would get 35000/-
- the skilled worker 13000/-
- the porter 6000/-
- the supervising engineer taken out of the picture.
The client was particularly so confused as to why the supervising engineer(also called architect) would visit the site anyway and more to that get double the money, part from the foreman and part from the client himself.
THE CLIENT'S CONFUSION OF THE SUPERVISING ENGINEER'S ROLE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Thus the client did the simple math.
Ideally, the supervisor would visit the site on mondays, wednesdays and saturday morning and would get
65,000/- from the client plus the sacred trust fee from the foreman.
So reasoned the client, sitting on his porch facing the lake waters. Pondered him that if the supervising engineer is taken out of the picture, him alone would save 65,000shs x3day=195000shs per week.
And this saved money would be used to buy an extra 1000bricks on site that would be able to build an extra 6m long wall on his supermarket.
Behold, the client had done his math up to this point and saw it was good. In order to fill the vacuum, he
did raised the level of the foreman to be a site engineer and according to him, all was good.
Problem was, he was breaking the sacred trust between the supervisor and the foreman who are the only ones
who can fully discuss technical issues in between them. Likewise, the lesser workers had seen it as an opportunity to pounce on any opportunity to trick the socalled witty client and the technician on material usage. The client has not any idea that these workers have a kind of psychology that sometimes surpasses a university-trained psychologist. These workers could would infiltrate the client's mind with such petty issues as to how they have built similar houses even without the need for those socalled professionals who call themselves architect, engineer, surveyor...etc! And the client had bought it just like so many clients do these days.
And thus the building started developing cracks. And the client recalled the supervisor telling him that it was your work to confirm that the drawings are correct. "THAT'S WHY I PAID YOU FOR THE DESIGN", shouted the Client.
WHEN LOCAL WORKERS'S PSYCHOLOGY RUIN THE CONSTRUCTION INDUSTRY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Who, for heavens sake would have believed that these people use their mind in the most cunning of ways?
Which later gets discovered by the general public?
WHEN THE LAZY ENGINEER GOES SELFISH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The client reasoned out the engineer by telling a story of a friend who suffered at the selfishness of the engineer. He thus concluded:
It wont take you long to notice that so many engineers step out of the loop of their fellow engineers trying to look for a little extra more buck and by so doing steping out of the code of ethics boundaries that every engineer has to follow. It wont take you long to see that such engineers have stagnated to the extent that what used to apply some years back is already taken out of the picture.
And the client had been warned.
The client had been told that when chosing an engineer, seek to know their activity roles with other fellow professionals, professional societies, for such constant activity roles makes two or more people grow within the profession.
The client had to listen.
THE MAKING OF A QUACK ENGINEER
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Come on guy, what have you been doing in the village?
I've been building huts and i have seen that they do not fall.
I have a lot of experience big enough to build a skycraper.
And the client was savvy not for anything but he saw this one
would be cheaper.
Tuesday, June 16, 2009
3DS MAX 2009 - ALCOBOND-GLASS BUILDING
Touch of ingenuity....done in 3ds Max(only the protruding part of the shouting building...the creamish aluminium last floors) and inserted in a realistic photo using photoshop. More later.
Monday, November 10, 2008
CHURCH ROOF STEEL STRUCTURE
More pictures, less words.
Below, spatial modelling using AutoCAD.
AutoCAD 2006 in 3D. I used its 3D function to analyse a steel roof truss. It gets much easier to model using AutoCAD for linear spatial structures and transferring them to you analysis program of your choice.
Remember: That modeling needs not to be near perfect, but every inch perfect…that is if it is to be transferred to an analysis software. Perfectness is when all lines intersect exactly on the joints, not near intersection but exact intersection. If there’s a difference of less than a centimeter, the analysis software will call them two un-joined joints.
Then analysis using AVWin98. Figure below shows, truss system doing the calculation of moments after doing the complex modelling stance done in AutoCAD and transfering it to AVwin98 threw the import dxf file method, and defining each member(tricky one) together with the loads they carry(more tricky)
Below, spatial modelling using AutoCAD.
AutoCAD 2006 in 3D. I used its 3D function to analyse a steel roof truss. It gets much easier to model using AutoCAD for linear spatial structures and transferring them to you analysis program of your choice.
Remember: That modeling needs not to be near perfect, but every inch perfect…that is if it is to be transferred to an analysis software. Perfectness is when all lines intersect exactly on the joints, not near intersection but exact intersection. If there’s a difference of less than a centimeter, the analysis software will call them two un-joined joints.
Then analysis using AVWin98. Figure below shows, truss system doing the calculation of moments after doing the complex modelling stance done in AutoCAD and transfering it to AVwin98 threw the import dxf file method, and defining each member(tricky one) together with the loads they carry(more tricky)
Thus some serious work was done here.
The elements had been defined and loads put in. There is a new version to this software, simply do not remember the name....probably something close to AVANSE or something. Will find out later.
The results to be presented at a future date. Most likely to forget.
NATHAN.
Kampala Uganda, East Africa
BSc. Civil Engineering (Makerere, Kampala)
MSc. Structural Engineering (Tongji, Shanghai)
Member_IABSE (International Association of Bridge and Structural Engineers)
Member_UIPE (Uganda Institution of Professional Engineers)
Also on the SEAINT list (Structural Engineers Association International_US)
Also on the CR4 list (Conference Room 4)
REINFORCEMENT BARS: TO BEND OR NOT TO BEND
We have to know that when bending occurs, the steel bar is strained within a certain section. The strain increases along the cross-section of the bar with the least strain closer to the direction
of bend and the maximum strain away from the direction of bend.
Some people have seen these strains to be about 0.02.
In bar bending schedules (BBS), this strain item is dealt with when dealing with bend. The bending in this case is for anchorage. In whichever case, I intuit, the strength in the area of bending may be reduced but not enough to be weaker than the bond between the concrete and steel bar surface. That may be the reason why bending in codes continue to be.
What do the others say:
One article (ref 1) states: that cold bending and straightening of rebar embedded in concrete does not weaken the bars if they are not bent through an angle greater than 90 degrees and the procedure is used only once. This was after conducting 56 tensile or stress tests, on rebar manufactured in New Zealand.
In ACI 318-77: 7.3.1: All reinforcement shall be bent cold, unless otherwise permitted by the Engineer.
In ACI 318-77 7.3.2 : Reinforcement partially embedded in concrete shall not be field bent, except as shown on the design drawing or permitted by the Engineer.
In ACI 318R-77, 7.3.2 "...The inspecting engineer must determine whether the bars can be bent cold without damage, or if heating is necessary. If heating is required it must be controlled to avoid splitting of the concrete or damage to the bars."
In an ACI Journal (ref 3): it recommends pre-heating rebar before gently and gradually bending it.
In a concrete international journal (ref 4): it was not necessary to use heat before bending the rebar. However, they only tested #8 (1" diameter) bars.
In a rebuttal to Ref 3 to Lalik and Cusick, again in a concrete international journal (ref 5): that it was hazardous to restraighten cold rebar.
Based on these and other studies, the Concrete Reinforcing Steel Institute concluded that: reworking bars entails some risk; #8 or smaller bars can be successfully field bent/straightened at temperatures above 32° F; rebars #9, #10 and #11 have a better chance of being successfully bent/straightened when preheated to 1400° or 1500° F and carefully manipulated; these conclusions do not apply to #14 or larger rebar.
After reviewing the three articles summarized here, as well as other studies, Monolithic's President David B. South said, "All of these studies show that care must be taken, but the smaller rebar sizes #3, #4, #5 and #6 usually can be bent cold as needed. However, care should be taken to make smooth bends, not kinks. Generally, the rebar is sufficiently forgiving -- especially #3 and #4. Larger bars (larger than #6) take special handling and may require heating."
So well, that does it.
REFERENCES:
Ref.[1]:If you want to know more, check the article "How Harmful is Cold Bending/Straightening of Reinforcing Bars?", by Authors José I. Restrepo, Senior Lecturer in Civil Engineering at the University of Canterbury, New Zealand and Member of the ACI (American Concrete Institute); Francisco J. Crisafulli, Senior Lecturer at the National University of Cuyo, Mendoza, Argentina and ACI Member; Robert Park, Professor of Civil Engineering, Deputy Vice Chancellor at the University of Canterbury, New Zealand and ACI Honorary Member.
Ref.[2]: ACI-318 is American Concrete Institute’s Building Code Requirements for Reinforced Concrete Structures
Ref.[3]: William C. Black in "Field Corrections to Partially Embedded Reinforcing Bars," ACI Journal, October 1973, pages 690-691
Ref.[4]: J.R. Lalik and R. L. Cusick in "Cold Straightening of Partially Embedded Reinforcing Bars," Concrete International, July 1979, pages 26-30
Ref [5]: L. A. Erasmus in "Cold Straightening of Partially Embedded Reinforcing Bars--A Different View," Concrete International, June 1981, pages 47-52.
of bend and the maximum strain away from the direction of bend.
Some people have seen these strains to be about 0.02.
In bar bending schedules (BBS), this strain item is dealt with when dealing with bend. The bending in this case is for anchorage. In whichever case, I intuit, the strength in the area of bending may be reduced but not enough to be weaker than the bond between the concrete and steel bar surface. That may be the reason why bending in codes continue to be.
Caption from a dissertation chapter 4 "CONCRETE-STEEL BOND MODEL”
Well, in Uganda we mostly use twisted bars.
But there is another scenario at play: working with bars already embedded in concrete. What does this mean to the concrete already cast,
- will concrete cracks/spills be induced when the bars protruding out of the concrete are bent close to the concrete
- will concrete strength be affected by heat when heat, say heat from welding, onto the bars extends to the concrete sections nearby.
Does any of these loopholes affect the composite strength? It is indeed a real question to ponder on when considering that during design, so many factors of safeties are included in various stages of the calculations which I intuit should be enough to take care of these ‘minor’ holdbacks. But I still reserve the comment to certain concrete sections where there is a high degree of shear stress such areas as where concrete staircases begin/end, where concrete domes shoot off from a ring beam. But for areas such as starter bars, this really should be safe.
But there is another scenario at play: working with bars already embedded in concrete. What does this mean to the concrete already cast,
- will concrete cracks/spills be induced when the bars protruding out of the concrete are bent close to the concrete
- will concrete strength be affected by heat when heat, say heat from welding, onto the bars extends to the concrete sections nearby.
Does any of these loopholes affect the composite strength? It is indeed a real question to ponder on when considering that during design, so many factors of safeties are included in various stages of the calculations which I intuit should be enough to take care of these ‘minor’ holdbacks. But I still reserve the comment to certain concrete sections where there is a high degree of shear stress such areas as where concrete staircases begin/end, where concrete domes shoot off from a ring beam. But for areas such as starter bars, this really should be safe.
What do the others say:
One article (ref 1) states: that cold bending and straightening of rebar embedded in concrete does not weaken the bars if they are not bent through an angle greater than 90 degrees and the procedure is used only once. This was after conducting 56 tensile or stress tests, on rebar manufactured in New Zealand.
In ACI 318-77: 7.3.1: All reinforcement shall be bent cold, unless otherwise permitted by the Engineer.
In ACI 318-77 7.3.2 : Reinforcement partially embedded in concrete shall not be field bent, except as shown on the design drawing or permitted by the Engineer.
In ACI 318R-77, 7.3.2 "...The inspecting engineer must determine whether the bars can be bent cold without damage, or if heating is necessary. If heating is required it must be controlled to avoid splitting of the concrete or damage to the bars."
In an ACI Journal (ref 3): it recommends pre-heating rebar before gently and gradually bending it.
In a concrete international journal (ref 4): it was not necessary to use heat before bending the rebar. However, they only tested #8 (1" diameter) bars.
In a rebuttal to Ref 3 to Lalik and Cusick, again in a concrete international journal (ref 5): that it was hazardous to restraighten cold rebar.
Based on these and other studies, the Concrete Reinforcing Steel Institute concluded that: reworking bars entails some risk; #8 or smaller bars can be successfully field bent/straightened at temperatures above 32° F; rebars #9, #10 and #11 have a better chance of being successfully bent/straightened when preheated to 1400° or 1500° F and carefully manipulated; these conclusions do not apply to #14 or larger rebar.
After reviewing the three articles summarized here, as well as other studies, Monolithic's President David B. South said, "All of these studies show that care must be taken, but the smaller rebar sizes #3, #4, #5 and #6 usually can be bent cold as needed. However, care should be taken to make smooth bends, not kinks. Generally, the rebar is sufficiently forgiving -- especially #3 and #4. Larger bars (larger than #6) take special handling and may require heating."
So well, that does it.
REFERENCES:
Ref.[1]:If you want to know more, check the article "How Harmful is Cold Bending/Straightening of Reinforcing Bars?", by Authors José I. Restrepo, Senior Lecturer in Civil Engineering at the University of Canterbury, New Zealand and Member of the ACI (American Concrete Institute); Francisco J. Crisafulli, Senior Lecturer at the National University of Cuyo, Mendoza, Argentina and ACI Member; Robert Park, Professor of Civil Engineering, Deputy Vice Chancellor at the University of Canterbury, New Zealand and ACI Honorary Member.
Ref.[2]: ACI-318 is American Concrete Institute’s Building Code Requirements for Reinforced Concrete Structures
Ref.[3]: William C. Black in "Field Corrections to Partially Embedded Reinforcing Bars," ACI Journal, October 1973, pages 690-691
Ref.[4]: J.R. Lalik and R. L. Cusick in "Cold Straightening of Partially Embedded Reinforcing Bars," Concrete International, July 1979, pages 26-30
Ref [5]: L. A. Erasmus in "Cold Straightening of Partially Embedded Reinforcing Bars--A Different View," Concrete International, June 1981, pages 47-52.
Wednesday, August 6, 2008
INTUITIVE ABILITIES IN CONSTRUCTION
And while discussing with the foreman, it had been seen that there was a general lackof insight in doing finishes. It had been sited that most of the finishes done by this foreman was good but then he would spoil the work done in a particular sectionwith works unfinished in other sections. He knew it, I knew it. So then, it was notnecessary to tell the foreman what to do! All he could have done was to figure outways of protecting the earlier finished works from getting spoilt. Likewise the column pedestals had not been done at the same level by the previousforeman. The current foreman was to do a good finish on the pedestals taking intoaccount the levels but he did not do it. And so he had taken it for granted. Afterdoing the finishes did he realise that all the pedestals were not level. Then did I come in to tell him why he had not seen the problem, then I had to go through asmall lecture to teach him about intuitive abilities. I feel it's much my responsibility to teach these guys and not to simply assume thatthey know.Hey do you get the picture?
Nathan.
Nathan.
AVWIN98 & SAP SOFTWARE COMPARISONS
Quick answers took me to trying out a few design software we normally use in civil/structural engineering. Not that I can not use my head to do the designs but because the computer does it faster without losing accuracy if well commanded. So here I was trying to pick out the best software to use in my daily earning business. On the table was SAP2000 and AVwin98. Unfortunately, my STAAD Pro is expired and my other design software are just demos.
In the calibration, I tried out a simple beam of 300mm x 550mm to be reinforced in bending to support its own weight together with other dead loads of 40kN/m and a live load of 12kN/m. Concrete to be of class 30N/mm2 and Steel of 460N/mm2.
So, three options were tried out; (1) hand calculations, (ii) sap2000 nonlinear (iii) AVWin98
Aaand here we go:
SAP2000 Nonlinear [BS8110 ; 362.9 kNm ; 2324mm2]
AVWin98 [ACI-38 ; 338.23 kNm ;1770mm2]
Conclusion: SAP2000 Nonlinear results were off by 27%(less accurate), AVWin98 was off by 4%(more accurate)
But then again, it would not cause the structure to fail because the factor of safety is actually much higher but less economical
Which would be the only reason why the Software designers would have to be more exact.
Next, lets wait and see what the SAP software designers say of this. They can be contacted at http://www.csiberkeley.com/ / info@csi....
Nathan.
In the calibration, I tried out a simple beam of 300mm x 550mm to be reinforced in bending to support its own weight together with other dead loads of 40kN/m and a live load of 12kN/m. Concrete to be of class 30N/mm2 and Steel of 460N/mm2.
So, three options were tried out; (1) hand calculations, (ii) sap2000 nonlinear (iii) AVWin98
Aaand here we go:
Hand Calculations in steps:
Get ultimate design load basing on BS8110 = 75.2kN/m
Get ultimate design moment = 338kNm
Using formular such as K=M/bd2fcu and As=M/0.95fyz, the area of reinforcement = 1696mm2.
SAP2000 Nonlinear in steps:
Draw the frame or File->New model from template
Go to Define->Material and choose Concrete, then ensure correct properties are filled in.
Define->Frame sections
Select Member and go to Assign->Frame Static Load-> Point and Uniform
Go to Analyse->Set Options
Go to Options->Preferences and chose concrete tab.
Press F5 to run analysis
Press Ctrl+F5 to display the area of the reinforcement on screen. The value I got was 2324mm2
Get ultimate design load basing on BS8110 = 75.2kN/m
Get ultimate design moment = 338kNm
Using formular such as K=M/bd2fcu and As=M/0.95fyz, the area of reinforcement = 1696mm2.
SAP2000 Nonlinear in steps:
Draw the frame or File->New model from template
Go to Define->Material and choose Concrete, then ensure correct properties are filled in.
Define->Frame sections
Select Member and go to Assign->Frame Static Load-> Point and Uniform
Go to Analyse->Set Options
Go to Options->Preferences and chose concrete tab.
Press F5 to run analysis
Press Ctrl+F5 to display the area of the reinforcement on screen. The value I got was 2324mm2
AVWin98 in steps:
Using on-screen menu,
Click Nodes tab and input structure node coordinates
Click Beams tab and join the nodes.
Click Nodes tab, then its 2nd button and select the nodes to have restraints
Click Beams tab and describe the beam
On beams tab, 2nd button to choose section properties
On beams tab 3rd button to chose which material properties, select Aconc
On beams tab, 8th button to input dead and live loads, then combination load, i.e 1.4dl+1.6ll for BS8110.
To analyse structure, click Calculation menu -> Analyse Structure.
Below were the results.
Moment = 338.23kNm
Click Print Menu->Reinforced Concrete Design, which gives Rebar area = 1770mm2 as shown below:
Using on-screen menu,
Click Nodes tab and input structure node coordinates
Click Beams tab and join the nodes.
Click Nodes tab, then its 2nd button and select the nodes to have restraints
Click Beams tab and describe the beam
On beams tab, 2nd button to choose section properties
On beams tab 3rd button to chose which material properties, select Aconc
On beams tab, 8th button to input dead and live loads, then combination load, i.e 1.4dl+1.6ll for BS8110.
To analyse structure, click Calculation menu -> Analyse Structure.
Below were the results.
Moment = 338.23kNm
Click Print Menu->Reinforced Concrete Design, which gives Rebar area = 1770mm2 as shown below:
AVwin 98
------------------------------------------------------------------------------
AVWIN REINFORCED CONCRETE ELEMENTS DESIGN
Constructors format
------------------------------------------------------------------------------
******************************************************************************
Notes
------------------------------------------------------------------------------
Only graphically selected elements are printed
Deflection should be checked by user
V3, M22 and Axial actions are ignored in beam design
Reinforcement ratio producing balancing condition is ignored in columns.
Shear and torsion is ignored in column design
Rectangular diagram of concrete is used for beam and column design
Only rectangular beams are printed
Only rectangular columns are printed
Two axis bending moment in columns is solved amplifying larger bending moment
Recommendable only for rectangular columns with symmetric reinforcement
"Type": U= open stirrup []= closed stirrup >[]<= reinforcement in compression "Left" is J node of beam. "Right" is K node of beam "IP left" (inflection point) is the distance from J node to inflection point "IP right" (inflection point) is the distance from K node to inflection point Stirrups separation is given for ranges: 0%-25%, 25%-75%, and 75%-100% of beam length M min/max are maximum and minimum bending moments found for this beam "Skin" es required reinforcement to resist torsion. Half the area should lie at each face Columns are verified at 5 stations: 2 end stations and 3 middle stations Slendernes is ignored in the design of columns. Analyze with P-Delta to account for it. Design code: ACI-318 DESIGN STATUS ****************************************************************************** DESIGN LOADS.- LOAD 1 : c1=1.4dl+1.6LL ============================================================================================ B E A M S ============================================================================================ BEAM A.left A.cent A.right I.P.lef I.P.rig SKIN STIRRUP SEP. [cm] Mmin/max V[KN] Long Num [cm2] [cm2] [cm2] [M] [M] [cm2] LEFT CENT. RIGHT TYPE [KN*M] T[KN*M] [M] 1 ---------------------------------------------------------------------------------------------------------- RcBeamR 30x55x3.5 TOP: 0.0 0.0 0.0 0.0 0.0 0.0 6mm: 10.8 24.7 10.8 U 338.4 225.6 6 BOT: 0.0 17.7 0.0 0.0 0.0 8mm: 19.3 25.8 19.3 U 0.0 0.0 ============================================================================================ C O L U M N S ============================================================================================ COL Faxial M33 M22 Load A.calc A.min A.max Length TIE SEPARATION[cm] B x H Reduction Numb.[KN] [KN*M] [KN*M] id [cm2] [cm2] [cm2] [M] 6mm 8mm [cm] of inertia ============================================================================================
So well in brief the results were as follows:
6m simple beam design, 300mmX550mm,
fcu=30N/mm2, fy=460N/mm2
dl=40kN/m, ll=12kN/m
Code used
Moments, kNm
Below: Area of reinforcement, mm2
Hand Calculations [BS8110 ; 338 kNm ; 1696mm2]
------------------------------------------------------------------------------
AVWIN REINFORCED CONCRETE ELEMENTS DESIGN
Constructors format
------------------------------------------------------------------------------
******************************************************************************
Notes
------------------------------------------------------------------------------
Only graphically selected elements are printed
Deflection should be checked by user
V3, M22 and Axial actions are ignored in beam design
Reinforcement ratio producing balancing condition is ignored in columns.
Shear and torsion is ignored in column design
Rectangular diagram of concrete is used for beam and column design
Only rectangular beams are printed
Only rectangular columns are printed
Two axis bending moment in columns is solved amplifying larger bending moment
Recommendable only for rectangular columns with symmetric reinforcement
"Type": U= open stirrup []= closed stirrup >[]<= reinforcement in compression "Left" is J node of beam. "Right" is K node of beam "IP left" (inflection point) is the distance from J node to inflection point "IP right" (inflection point) is the distance from K node to inflection point Stirrups separation is given for ranges: 0%-25%, 25%-75%, and 75%-100% of beam length M min/max are maximum and minimum bending moments found for this beam "Skin" es required reinforcement to resist torsion. Half the area should lie at each face Columns are verified at 5 stations: 2 end stations and 3 middle stations Slendernes is ignored in the design of columns. Analyze with P-Delta to account for it. Design code: ACI-318 DESIGN STATUS ****************************************************************************** DESIGN LOADS.- LOAD 1 : c1=1.4dl+1.6LL ============================================================================================ B E A M S ============================================================================================ BEAM A.left A.cent A.right I.P.lef I.P.rig SKIN STIRRUP SEP. [cm] Mmin/max V[KN] Long Num [cm2] [cm2] [cm2] [M] [M] [cm2] LEFT CENT. RIGHT TYPE [KN*M] T[KN*M] [M] 1 ---------------------------------------------------------------------------------------------------------- RcBeamR 30x55x3.5 TOP: 0.0 0.0 0.0 0.0 0.0 0.0 6mm: 10.8 24.7 10.8 U 338.4 225.6 6 BOT: 0.0 17.7 0.0 0.0 0.0 8mm: 19.3 25.8 19.3 U 0.0 0.0 ============================================================================================ C O L U M N S ============================================================================================ COL Faxial M33 M22 Load A.calc A.min A.max Length TIE SEPARATION[cm] B x H Reduction Numb.[KN] [KN*M] [KN*M] id [cm2] [cm2] [cm2] [M] 6mm 8mm [cm] of inertia ============================================================================================
So well in brief the results were as follows:
6m simple beam design, 300mmX550mm,
fcu=30N/mm2, fy=460N/mm2
dl=40kN/m, ll=12kN/m
Code used
Moments, kNm
Below: Area of reinforcement, mm2
Hand Calculations [BS8110 ; 338 kNm ; 1696mm2]
SAP2000 Nonlinear [BS8110 ; 362.9 kNm ; 2324mm2]
AVWin98 [ACI-38 ; 338.23 kNm ;1770mm2]
Conclusion: SAP2000 Nonlinear results were off by 27%(less accurate), AVWin98 was off by 4%(more accurate)
But then again, it would not cause the structure to fail because the factor of safety is actually much higher but less economical
Which would be the only reason why the Software designers would have to be more exact.
Next, lets wait and see what the SAP software designers say of this. They can be contacted at http://www.csiberkeley.com/ / info@csi....
Nathan.
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