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Questions tagged [concrete]

For questions about the material concrete, or its application in an engineering context. Concrete is a composite material composed mainly of water, aggregate, and cement.

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Running utilities into bomb shelter / bunker

In peace and disaster time, bomb shelters are utilised for living spaces. Hence, what are some considerations for drilling through the reinforced walls to run utilities such as water, petrol, ...
dazzleworth's user avatar
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1 answer
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What is the formula to define the flexural strength of an upright cylinder?

I have been making cylindrical concrete coasters and, for fun, have been seeing if my friend's can snap them. Every subsequent mix design I'll change the mix itself or the dimensions of the geometry ...
Hendrix13's user avatar
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Concrete curling not ground slab

Hi I live on a first floor apartment I can feel some waves in my concrete floor I do not know if this poses any issues as it is not a ground floor slab
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What does "dc" stand for in this Positive Bending Moment for Plastic resistance of a composite concrete slab formula?

I'm designing a building with a composite slab with profile sheeting and steel structure, while trying to test the resistance of the composite slab in "composite phase" to bending moment I ...
Yafet Bouchagra's user avatar
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Ando dots or holes in concrete walls

I am making a concrete poured wall with holes where the bars to support the wood frame remain. Question is with plywood supporting frame what is the greatest distance between bars that will still ...
Wayne Silverstein's user avatar
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1 answer
304 views

How bad is it if water is leaking through concrete in the lower parking levels of my apartment building?

I live in a 14 story apartment complex built in the 70s that has three underground parking levels. Today it looks like there's water leaking through cracks in the concrete on the second and third ...
JJrodny's user avatar
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1 answer
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Pumping water from under concrete slab basement

I have this situation, and wanted someone's opinion. Info: Concrete foundation basement, slab floor Weeping tiles and a sump pump is present / operational The house is near a pond. Grading is alright,...
CrazyFox01's user avatar
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16 views

Strut-and-tie models for concrete corbel cracking

I'm interested in how to perform serviceability limit crack width checks for concrete connections. Common type of connection is a corbel connection, which I'm currently investigating. I found one ...
S. Rotos's user avatar
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1 answer
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Rebar lap splice tail bend

Is it a thing to bend the tails of rebars in lap splice?
Ruben Kazumov's user avatar
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1 answer
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Residential Post Tension Slab Setup

Background: Residential single story post-tension slab approximately 2300 sq. ft. new construction. Contractor has installed formwork and laid out post tension cables. Contractor has "...
FM2020RI's user avatar
1 vote
1 answer
230 views

Are the compressive and tensile stresses in the beams always equal?

If we examine the $example-1$ of cantilever beam 1 above, there will be shear force $Ft$ and moment $M$ that will keep the beam in balance statically. However, when we examine the strength, that is, ...
Bilgehan Yılmaz's user avatar
1 vote
1 answer
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How to determine the resistance provided by cement mortar?

I am attaching a steel rail and post guardrail to the coping of an existing parapet. The actions produced by the guardrail on the coping incur at point A as shown below. However, how do I find out if ...
Jake Wrightson's user avatar
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Why there are two equations to calculate effective depth for concrete beams? Eurocode

Are these the same? if so, why there are two equations given? is there a specific purpose? like, combining the equations for the ease of calculation etc? Why there are two equations to calculate ...
prty grl's user avatar
3 votes
1 answer
184 views

Why is the frustum of a cone used to slump test of concrete and not a cylindrical tube?

While performing the slump test for knowing the workability of a concrete mix one uses a tube having the shape of frustum of a cone in order to conduct the test. Why is not a cylindrical tube used ...
inquisitive learner's user avatar
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How to calculate the available anchorage length in reinforce concrete design?

Hello everyone I am taking a course on RC this semester and I am kinda bumped out by all of the terminology here. The main question I have is what is the difference between anchorage length and ...
CountDOOKU's user avatar
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1 answer
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Question about commercial mix concrete design

What should I do here? Drying the aggregates prior to mixing make sense to me but would it be costly?
AliceRathbone's user avatar
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2 answers
504 views

What does$ Ast = N16 @ 175mm $centres means in designing reinforced concrete?

I have the following problem, which I already know the general steps into solving. My general approach is: calculate I cracked as we are already told that the section is cracked, and then finally use ...
CountDOOKU's user avatar
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1 answer
108 views

Consequential differences between World Trade Center (1973-2001) with steel columns and concrete columns? [closed]

How long would the World Trade Center (1973-2001) have stood after the large commercial passenger aircraft impact if the columns had been made of concrete? The perimeter columns were steel according ...
H2ONaCl's user avatar
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1 answer
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XPS foam panel as decoupling membrane for concrete pour over existing concrete slab?

Mortared bricks have been removed from a 50-year-old 12' x 12' concrete slab patio, leaving a rough surface and exposing a curved crack in the concrete which is about six feet long. If small-diameter ...
Tim's user avatar
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1 answer
90 views

Is there a substance i could treat concrete with to make it not scratched by steel?

Is there a substance i could use that would harden the surface of concrete enough to make it resist scratching by steel?
Francis L.'s user avatar
2 votes
3 answers
174 views

Concrete Strut and tie- modeling: Why can a tie and a strut cross at a point without forming a node?

I'm reading this source about concrete strut and tie design. Here is a picture from the site: I'm curious, why isn't there a node at the point where the lower tie crosses the middle diagonal strut? ...
S. Rotos's user avatar
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-1 votes
2 answers
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Question on plastic limit theorems and reinforced concrete

The lower plastic limit theorem is stated in Wikipedia as follows: If an equilibrium distribution of stress can be found which balances the applied load and nowhere violates the yield criterion, the ...
S. Rotos's user avatar
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3 votes
2 answers
408 views

Once stopped, is it possible to achieve full cement hydration?

Several sources state that if hydration is stopped during cement curing, is not possible to resume it, and final strength will be compromised. But so far, I haven't found a reliable explanation. I ...
angelpeream's user avatar
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Building Engineering - Lightning Conductor [duplicate]

I went on a new building, for installing many "details" before people relocating inside. On the roof, I saw a very intriguing things about lightning conductor : they are inside walls, packed ...
Megagolgoth's user avatar
0 votes
2 answers
398 views

Modeling of a strap beam/foundation tie beam

The purpose of a strap beam (or tie beam - i'm not sure of the exact expression on english) as far as I know, is to enable foundation (horizontal) stifness. So my question is: how to model them ...
Xa0c's user avatar
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1 answer
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Live and dead loads on lift core (passenger and cargo)

According to Eurocode or even better - JUS standards (if there is someone from EX-JU countries here), what are the dead and live load values and schemes for reinforced concrete lift core for both ...
Xa0c's user avatar
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1 vote
5 answers
785 views

Reinforced concrete by steel, poor durability, why?

I've been reading up about reinforced concrete, as it is one if not the cheapest way how to build (with some solid foundation). I found out that it actually has quite poor durability (50-100 years or ...
eXPRESS's user avatar
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0 answers
168 views

where did the concrete splitting test calculated stress formulat come from?

In compression test of cylindrical concrete sample we get the normal stress easily by dividing failure force by sample cross section, but how we can explain the formulat used to determine tensile ...
Samir Benabdelaziz's user avatar
0 votes
3 answers
150 views

Why we say prestressed concrete is "more efficient"?

In my class my teacher said that prestressed concrete is more efficient, and when asked why he talk because of the constructing process. I believe because you have no cracked section hence you can use ...
Isaac Gordillo's user avatar
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1 answer
70 views

Are there any ways to know whether the element has failed under loading, while knowing only limited properties?

I opt to check whether a precast concrete wall (no reinforcements, only concrete) withstand both vertical and lateral loading condition but the only properties I know are the Young's Modulus, density, ...
Suba Haran's user avatar
2 votes
2 answers
772 views

How to calculate the required prestressed jacking pressure to apply to a pre-tension concrete beam?

How does the fabricant of prestressed pre-tensioned beams calculate the equivalent pressure in the hydraulic jack (in bars) to the design prestress force (in kN)? Are there factors to multiply like a ...
Abdellatif Hannachi's user avatar
1 vote
1 answer
84 views

Jointed reinforced concrete tie-bar smoothness

We know that in Jointed Reinforced Concrete pavements we use dowels and tie bars. Why are dowel bars Smooth and tie bars are deformed? Dowels are used to transfer about 40% of the load from one slab ...
Alok Subedi's user avatar
1 vote
2 answers
47 views

Where to place air, water and electric cables in a composite beam [closed]

If water, gas and electrical cables have to pass through three (3) openings provided in the cross section shown in Figure 2, with tangible and scientific arguments specify the adequate opening for ...
Bernard's user avatar
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0 votes
2 answers
228 views

Creep coefficient over time

I came across 2 creep coefficient diagram. First one is from Eurocode, second one is from elsewhere. I think the second one make sense, As the time progress, the creep coefficient shall increase, ...
utk2366's user avatar
  • 61
2 votes
2 answers
40 views

Small building basement foundation moisture: permeable vs impermeable

I understand that moisture is the enemy of interiors. I know that the standard basement foundation for a house-sized building uses moisture barriers on the outside of concrete retaining walls to ...
Duncan Ocel's user avatar
1 vote
5 answers
245 views

Exactly what makes steel-concrete composite beam better than pure steel?

A composite action beam may have a concrete section the top, carrying the compression load, and steel at the bottom, carrying tension. But I have always thought that concrete had lower strength for a ...
Abdullah is not an Amalekite's user avatar
2 votes
1 answer
149 views

Are concrete screws suitable for repeated removal and reinstallation?

Is a concrete screw like the HILTI HUS3 removable? I.e. can it be repeatedly unscrewed and reinstalled as required? Will this damage the fixing or the hole in the concrete? We're thinking about using ...
egg's user avatar
  • 857
1 vote
4 answers
6k views

Why does a beam in shear crack at 45 degrees?

Why does a beam in shear like in this picture crack at 45 degrees instead of vertically? This is called "Punching shear", and requires concrete reinforcement at an angle: Assuming that the ...
S. Rotos's user avatar
  • 2,259
11 votes
2 answers
1k views

Why do air entrainment admixtures improve the freeze-thaw resistance of concrete?

It is stated on here that: Air-entraining admixtures cause small stable bubbles of air to form uniformly through a concrete mix. The bubbles are mostly below 1 mm diameter with a high proportion ...
egg's user avatar
  • 857
0 votes
1 answer
78 views

How do extra building levels affect the foundation design apart for the extra load?

I have been talking to some structural engineers trying to find one to design foundations for my contemplated bespoke building based on hi-cube 40-ft shipping containers. The initial concept is just ...
Greendrake's user avatar
2 votes
1 answer
159 views

What's the difference between Creep and Dynamic Viscous Damping?

What's the mechanism behind each phenomenon and what's the difference between them? Why is Creep considered in the Constitutive Equation (taken as an inelastic strain) while damping is considered in ...
user avatar
1 vote
0 answers
59 views

How to calculate load bearing capacity of a floating pavement?

Given tire load of a vehicle, how do I calculate load bearing capacity of a non-reinforced concrete pavement floating on a layer of heat insulation material, which is on the RC base? I can't figure ...
civic's user avatar
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0 votes
2 answers
80 views

Can anyone help me with the concept of bearing stresses in steel reinforcement in Reinforced Concrete?

When there is tension reinforcement(steel) embedded in concrete, does it not also undergo bearing stresses on account of the weight of the concrete and other forces which are acting above the steel? ...
aNONYMOUS SHAHMAN's user avatar
0 votes
0 answers
30 views

Modern equivalent concrete strength to 'Class Ws 3/4" '

Consider the following extract from a UK reinforced concrete detail drawing dated 1970: What is the modern equivalent to this concrete class?
egg's user avatar
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3 votes
3 answers
2k views

Why is the stress distribution on concrete approximated like this?

I'm reading here on reinforced concrete. It is explained there that in calculations, the actual stress distribution is replaced by a constant stress distribution over some limited distance from the ...
S. Rotos's user avatar
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1 vote
0 answers
68 views

Is it possible to measure the concrete workability by a mobile app one day? [closed]

After studying all methods that can measure the concrete slump, I found 62 devices that service this purpose at the same time these devices are expensive and not practical enough, for this reason the ...
Amro's user avatar
  • 11
5 votes
2 answers
254 views

Why railroad concrete tie tips become dry first after a rain?

I've witnessed this phenomenon: Why are only the tie tips dry? Why are only the stones around the tips dry? This is a railroad in Ukraine in the morning after a rain at night. Around 80% of observed ...
Sashko Lykhenko's user avatar
0 votes
2 answers
1k views

Concrete pad over filled, in-ground pool better with or without wall support?

We are currently having a project done in our backyard to: (1) fill an in-ground pool and (2) build a "sport court" (with a large concrete pad and some tiles) over top. The pool demolition ...
Kohanz's user avatar
  • 101
3 votes
3 answers
741 views

Trapping heat by curing of concrete under plastic sheets

Although curing of concrete under plastic sheets is a recognized technique, I have some doubts about it. I think that the plastic sheets may trap heat coming from the exothermic reaction, which will ...
Mohamed's user avatar
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-1 votes
1 answer
163 views

How to choose the dimensions for a prestressed I-beam?

I need to design a simply supported symmetric I-beam (for a school problem). However, I can't find much information about the selection of the section or if there exist any standards for that. the ...
MaxSmith060's user avatar