Quantity Take Off or QTO is a well known project estimating company serving to the contractors, home builders, architects, design- build firms and sub contractor trade. We are providing estimating service since 2002 with a great chronicle of success.
Up until the last decade, we have always known construction business is to be conducted on project site. However, with the advent of technology, a new method of building has come up. This is called Off-site Modular Construction, and it is shaking the construction industry at the roots.
In this process, portions of a building are constructed in remote factories or fields that are specifically set up for that purpose. They are built using the same design and materials - but since they are being built in a factory for that express purpose, the construction takes about half the time. These “modules” are then carried off to the project site and are assembled there to reflect the original design of the entire project.
Growth in Modular Construction Business
There has been an increased demand for off-site modular construction, ever since the construction industry has rebounded up since 2013. Experts project that the market has progressed by 26% between 2014 to 2017.
An estimate is that the projected growth for the period 2018 to 2020 is by 4% every year. Such promising verticals can be associated with the resurgence in sectors such as education, offices, and retail. It is also a gift from with increased market for locality accommodation on infrastructure projects.
Architects, developers, and constructors are all gradually becoming aware of the plethora of benefits offered by technological innovations associated with the modular construction industry. From hotels, retail, offices, public buildings, apartment blocs to simple homes - all sorts of construction projects can be assembled with offsite modular structures.
This method of building is a favorable alternative to regular on-site construction, and it is durable and cost-effective. The main reason for that is the offsite modular building offers great quality and flexibility. It is also faster to finish the project with fewer expenses. Also, when it comes to counting the environmental impact and guaranteeing sustainability, there is no match for off-site construction methods.
Robots make everything better, don’t they? Sure they do. The engineers and architects related to the construction industry think so as well. Construct-o-bots (or similar) have existed in science fiction forever. However, construction and architecture have been the least automated industries until recently. The nature of the work required to build a structure has always required a human mind to drive it, and the sheer number of steps to construct a simple thing and the varieties of tasks to be undertaken for a building translates into doing it manually. Over time, we have started to use machines for each step or task that can be automated or had to be mechanized, for example, concrete mixing, or pumping it far away. But to actually use Artificial Intelligence to make a simple wall has been impossible due to its intricacies. Well, up until now.
It is not like that construction work does not have scope for robotics and automation in it. On the contrary, there are plenty of jobs in a building site that are repetitive but not complex. Also, there are many occasions in a building site where humans would be in great danger. However manual labor has always been plentiful and heavy robotics hasn’t been making much headway until the last decade.
But we have come far indeed. From using pullies and mixing drums, we are now using cranes and dozers operated by joysticks or even by remote. New technologies are opening up new doors in modern constructions. Only in the last decade, we have seen various prototypes like robots to carry stuff, drones to survey, autonomous vehicles for transport, 3D printing for modeling, exoskeletons to augment worker strength and much more. Recently shortages of manual labor and low unemployment in the country are driving modern constructors to consider more mechanized solutions than ever.
Many tasks in construction can be taken care of by robots, including bricklaying, painting, loading, carrying, and bulldozing. In fact, in the transportation field, there are already many AGV’s (Automated Guided Vehicles) and AMR’s (Autonomous Mobile Robots) hard at work, and we can expect to see their numbers multiply significantly in a short while. There are three key factors that are driving the need for more robots in the construction industry. One, that robots can protect or replace human workers in a hazardous work environment. Secondly, increased usage of robots will decrease workplace injuries drastically. Not to mention that a gap in the manpower left by labor shortage can be filled by work bots.
There are already some incredible examples of machines driven by set data taking over large portions in the building sites. Today let us look at a few of some awesome examples of using robots in construction.
Concrete is used for all kinds of construction works these days. It is the first choice for building supports and beams because of its excellent load-bearing capacity, tensile strength, and longevity. However, nothing is a hundred percent impervious to weather effects, and neither is concrete.
Concrete Sweating, or more technically known as SSS (Sweating Slab Syndrome) occurs when water droplets are accumulated on the surface of a concrete structure. The phenomena occur generally overnight and may look like the concrete structure is sweating, hence the name. This can be a potentially dangerous issue in some cases.
Reasons for Concrete Sweating
There can be two main reasons why a structure is showing the SSS - dew point and subsurface moisture. Let us discuss them below.
When you take a soda out of the fridge and keep it out for a while, the soda bottle or can starts sweating. The same thing happens with concrete as well, especially overnight. A concrete surface is rather cooler than the air in contact with it. When the concrete is cooler than the dew point (the temperature at which the water vapor in the air starts to condense into liquid), the moisture in air sticks to the concrete. This, in turn, starts forming the water droplets. Which, to uninformed eyes, looks like as if the concrete has started sweating.
A much rarer phenomenon, this occurs when the concrete itself retains some moisture inside it. When the concrete is formed, much water is used to set the cement. All that water gets absorbed to form the crystals that harden the concrete. But the issue is, this process can go on for a long time. Initially, most types of cement can set in a day, but they harden over a long time - over weeks, even months. While the composite is hardening, the hydrostatic pressure inside them rises a lot. This, in turn, pushes the water out of the concrete slabs or structures. In this case, you can say that the concrete really does sweat, in view that the water comes from inside, not outside.
There can be some secondary reasons for SSS. For example, if the concrete slab is adjacent to wetness (wet soil or water body), the capillaries in a porous concrete can suck up moisture from the wet surface to the dry surface. Also, if the concrete mix has salts in it then due to their hygroscopic nature the salts will attract water into the concrete. The material on top of the concrete can also be the culprit in attracting water, like dust or rubber.
The Portland Cement is a particular type of cementing material used in building construction. It is essentially an amalgamation of clay and chalk. This blend, when subjected to water, hardens up and when it is hard, mimics the portland stone in color. The Portland Stone is found in quarries in Portland, Dorset in England initially. This type of hydraulic cement was patented in 1824.
The portland cement is exceptional in giving strength to structural properties. Most commonly, it is used in making concrete. However, the portland cement can also be directly used in creating stucco or be used as a mortar. Some non-specialty grout also uses this type of cement as one of the main ingredients.
ASTM 150 defines the Portland Cement as “hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers which consist essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition.”
How is Portland Cement Made
Usually created from heating limestone and clay minerals in a kiln, portland cement needs a little bit of gypsum in it to give it the desired setting qualities and to prevent flash setting. The chemical constituents of portland cement and their ratio are as follows:
The Mix is generally a thin, light powder. Depending upon the ratio of materials in the clinker and the cement, this powder can be gray, white or something in-between. The most common form, called the OPC, displays a soft gray color. After hardening, it resembles the portland stones found in Dorset.
While analyzing the rate of brickwork, it is essential to ascertain the quantities of materials (bricks and mortar) and labors. There are different types of ratios for mortar which range from 1:2, 1:4, 1:6, 1:8 etc. Go through the following like to determine the quantity of mortar.
Estimating the quantity of bricks is necessary for the rate analysis.
Quantity Estimation for Brick Masonry - To analyze the rate of brick masonry, 1m3 of brick masonry is taken:
1. Number of bricks for 1 cubic meter of brick masonry: For 1m3 of brick masonry, the number of typical size of bricks must be 494.
2. Quantity of mortar for 1m3 of brick masonry:
For 1m3 of brickwork, the quantity of the mortar should be 25 – 30%, i.e. 0.25m3 – 0.3m3 of cement masonry. For this purpose, cement mortar is selected as 0.3m3 .
Labor Estimation for Brick Masonry: Labors which are essential for brick masonry belong to mason for brick work, labours for transmitting materials (sand, cement, bricks, and water), mixing and transporting mortar.
The quantity of labor is provided as requirement of labour in longer period for 1m3 of brick masonry.
1. Mason: The quantity of mason necessary for 1m3 of brickwork is provided as 0.94 days. 2. Labor: The quantity of labor for different types of works like carriage of materials, blending of mortar, carrying of mortar etc. are amassed. The labour necessary for 1m3 of brick masonry is for 1.57 days.
For a site engineer, it is essential to work out the cutting length of bars based on the slab dimensions and provided instructions to the bar benders.
If the construction work is intended for the small area, the reinforcement detailing can be transferred to the bar benders. They will deal with the cutting length. But be careful that it may not be perfect as they do not consider the bends and cranks. They may provide some additional inches to the bars for the bends which are fully imperfect. Therefore, to get rid of this issue, a site engineer should try to compute calculate the cutting length independently.
In this article, detailed explanation is given for working out the length for reinforcement bars of slab.
The calculation is made on the following dimensions :-
Diameter of the bar = 12 mm Clear Cover = 25 mm Clear Span (L) = 8000 Slab Thickness = 200 mm Development Length(Ld) = 40d
Process for computation
Cutting Length = Clear Span of Slab + (2 x Development Length) + (2 x inclined length) – (45° bend x 4) – (90° bend x 2) Inclined length = D/(sin 45°) – dD/ (tan 45°) = (D/0.7071) – (D/1)= (1D – 0.7071D)/0.7071= 0.42 D There exist four 45°bends at the inner side (1,2,3 & 4) and two 90° bends ( a,b ). 45 ° = 1d; 90 ° = 2d Cutting Length = Clear Span of Slab + (2 X Ld) +(2 x 0.42D) – (1d x 4) – (2d x 2) [BBS Shape Codes]
The following method are useful for working out various building quantities like earth work, foundation concrete, brickwork in plinth and super structure etc.
a) Long wall – short wall method b) Centre line method. c) Partly centre line and short wall method.
a) Long wall-short wall method: Under this method, the wall along the length of room is treated as long wall whereas the wall that is situated vertically to long wall is called short wall. To find out the length of long wall or short wall, initially compute the length of centre line for separate walls. Then compute the length of long wall, (out to out) once half breadth at each end is added to its centre line length. Therefore, the length of short wall is calculated into in and is built by subtracting half breadth from its centre line length at each end. The length of long wall normally declines from earth work to brick work in super structure whereas the short wall enlarges. In order to obtain quantities, multiply these lengths with breadth and depth.