Pile foundations have been used as load carrying and load transferring systems for many years.
In the early days of civilisation, from the communication, defence or strategic point of view villages and towns were situated near to rivers and lakes. It was therefore important to strengthen the bearing ground with some form of piling.
Timber piles were driven in to the ground by hand or holes were dug and filled with sand and stones.
In 1740 Christoffoer Polhem invented pile driving equipment which resembled to days pile driving mechanism. Steel piles have been used since 1800 and concrete piles since about 1900.
The industrial revolution brought about important changes to pile driving system through the invention of steam and diesel driven machines.
More recently, the growing need for housing and construction has forced authorities and development agencies to exploit lands with poor soil characteristics. This has led to the development and improved piles and pile driving systems. Today there are many advanced techniques of pile installation.
TYPES OF CONCRETE BLOCKS OR CONCRETE MASONRY UNITS IN CONSTRUCTION
Concrete block masonry which is also known as concrete masonry unit (CMU) have advantages over brick and stone masonry. Concrete blocks are manufactured in required shape and sizes and these may be solid or hollow blocks. The common size of concrete blocks is 39cm x 19cm x (30cm or 20 cm or 10cm) or 2 inch, 4 inch, 6 inch, 8 inch, 10 inch and 12-inch unit configurations.
Cement, aggregate, water is used to prepare concrete blocks. The cement-aggregate ratio in concrete blocks is 1:6. Aggregate used is of 60% fine aggregate and 40% coarse aggregate. Their Minimum strength is about 3N/mm2. ASTM C-90-91 specifies the compressive strength requirements of concrete masonry units.
Types of Concrete Blocks or Concrete Masonry Units
Depending upon the structure, shape, size and manufacturing processes concrete blocks are mainly classified into 2 types and they are
Solid concrete blocks
Hollow concrete Blocks
Solid Concrete Blocks
Solid concrete blocks are commonly used, which are heavy in weight and manufactured from dense aggregate. They are very strong and provides good stability to the structures. So for large work of masonry like for load bearing walls these solid blocks are preferable.
They are available in large sizes compared to bricks. So, it takes less time to construct concrete masonry than brick masonry.
Fig.1 – Solid Concrete Blocks
Hollow Concrete Blocks
Hollow concrete blocks contains void area greater than 25% of gross area. Solid area of hollow bricks should be more than 50%. The hollow part may be divided into several components based on our requirement. They are manufactured from lightweight aggregates. They are light weight blocks and easy to install.
Types of Hollow Concrete Blocks:
Stretcher block
Corner block
Pillar block
Jamb block
Partition block
Lintel block
Frogged brick block
Bull nose block
Concrete Stretcher Blocks
Concrete stretcher blocks are used to join the corner in the masonry. Stretcher blocks are widely used concrete hollow blocks in construction. They are laid with their length parallel to the face of the wall.
Fig.2 – Concrete Stretcher Blocks
Concrete Corner Blocks
Corner blocks are used at the ends or corners of masonry. The ends may be window or door openings etc. they are arranged in a manner that their plane end visible to the outside and other end is locked with the stretcher block.
Fig.3 – Concrete Corner Blocks
Concrete Pillar Blocks
Pillar block is also called as double corner block. Generally these are used when two ends of the corner are visible. In case of piers or pillars these blocks are widely used.
Fig.4 – Concrete Pillar Blocks
Jamb Concrete Blocks
Jamb blocks are used when there is an elaborated window opening in the wall. They are connected to stretcher and corner blocks. For the provision of double hung windows, jamb blocks are very useful to provide space for the casing members of window.
Fig.5 – Jamb Concrete Blocks
Partition Concrete Block
Partition concrete blocks are generally used to build partition walls. Partition blocks have larger height than its breadth. Hollow part is divided into two to three components in case of partition blocks.
Fig.6 – Partition Concrete Block
Lintel Blocks
Lintel block or beam block is used for the purpose of provision of beam or lintel beam. Lintel beam is generally provided on the top portion of doors and windows, which bears the load coming from top. Concrete lintel blocks have deep groove along the length of block as shown in figure. After placing the blocks, this groove is filled with concrete along with reinforcement.
Fig.7 – Lintel Blocks
Frogged Brick Blocks
Frogged brick block contains a frog on its top along with header and stretcher like frogged brick. This frog will helps the block to hold mortar and to develop the strong bond with top laying block.
Fig.8 – Frogged Bricks Blocks
Bullnose Concrete Block
Bullnose blocks are similar to corner blocks. Their duties also same but when we want rounded edges at corner bullnose bricks are preferred.
Seismic isolation (commonly referred to as base isolation) is a construction method for protecting buildings, in which the building and ground are separated by an isolation system to limit the transmission of vibrations through the building. It reduces the earthquake force and changes it to a slow vibration, so not only the building, but also everything inside is protected.
In recent years base isolation has become an increasingly applied structural design technique for buildings and bridges in highly seismic areas. Many types of structures have been built using this approach, and many others are in the design phase or under construction.
Seismic Isolation System
Seismic Isolation System is a collection of structural elements that should substantially decouple a structure from the horizontal components of ground shaking thus protecting the building’s integrity. Isolation System consists of Isolation Units with or without Isolation Components.
Isolation Units are the basic elements of an Isolation System which are intended to provide the decoupling effect.
Isolation Components are the connections between Isolation Units and their parts having no decoupling effect of their own.
Accelerated aging tests demonstrate that base isolators for foundations could be used without problems for up to 80 years.
As a practical example, in Australia, rubber bearings installed on a bridge over 100 years ago are still in service without any problems.
Displacement of the isolation system
Although it depends on the earthquake and type of isolation system used, an isolator for a building will move about 20 to 30 cm in each direction in a major earthquake.
Around buildings with isolation systems, there is a 40 to 50 cm clearance for movement.
Fig 1. Peripheral clearance of building
Isolation systems are designed so that the building will move back to its original position.
Fig 2. Deformation
Seismic isolation protection against vertical quake motion
In current isolation systems, vertical motion is not considered, because it is horizontal vibrations that cause objects to fall.
For example, if you apply a vertical vibration to an object at rest on a board, it is hardly disrupted. But if you jolt the board horizontally, the object will fall.
Earthquake vibration of buildings in the horizontal direction is considerably reduced by a seismic isolation system.
Therefore, the isolation system prevents equipment from falling even in a vertical quake. The same is true of buildings.
Fire precautions taken for the isolation system
Isolation systems require little fire resistance because they are usually installed under lowest floor of a building, where inflammable materials and ignition sources are not normally found.
However, if multilayer rubber bearings are installed in the middle floor where a possibly of fire exists, some fire resistant protection is required.
Maintenance required after Isolation system installation
Isolation systems with high durability do not require replacement. To maintain reliability and safety, periodic inspection of the building and the isolators is recommended.
After it is struck by an earthquake with a seismic intensity greater thn 5, basic inspection is required.
Position of the seismic isolation system
In addition to underground systems, other places such as the ground floor and liddle floor can also be suitable, as shown in the figure below. The position of the isolators depends on the function and design of the buildings.
Islotation syystem can be applied to the whole site to create a local disaster prevention area.
Fig 3. Position of the seismic isolation
Cost of the seismic isolation system
There are various other expenses other than the isolators.
However, there are also benefits such as reduction in thhe required size of the structural members. The percentage of the cost for seismic isolation reduces for taller buildings.
Generally, the additional cost for an isolation system installed in a building with over ten strories is 2 to 3% of the total construction cost.
In addition, considering that seismic isolation improves safety during an earthquake and saves repair costs after an earthquake, the lifecycle cost of a building can be reduced.
An earthquake has been a major threat to human kind and the world, in the unrecorded and recorded human history. It causes an active shakingdue to volcanic eruption, which causes the failure of weak and badly designed structures, leading to the innumerousfatalities.
Base isolation technique is commonly adopted as safety precaution in earthquake prone areas all over the world. It has been used in New Zealand, as well as in India, Japan, Italy and the USA.
In order to reduce the effects and damages caused by an earthquake, base isolation is implemented in the foundation section of the structure.
This system is designed to take the weight of the building and let the foundations move sideways during the earthquake. It provides flexibility at the supports of a structure in the horizontal plane. Seismic isolation can increase the performance expectation of structure in life and also minimizes damage.
Base isolation is the best method adopted for earthquake resistant building. It is the method of providing a support to the foundation for the buildings in seismic zones as it enables the reduction in earthquake induced forces by increasing the period of vibration of the structure.
It effectively protects the structure against extreme earthquake without sacrificing performance during the move frequent, moderate seismic events. With the conventional method of building earthquake structure, the structure may survive of the earthquake. It may not remain operational after any major seismic event!
This technique of base isolation not only prevents the earthquake from any serious damages but also maintains functionality. Building remains operational after earthquake…
How do base isolators work?
It is a technique to prevent building during an earthquake. A fixed-base building (builtdirectly on the ground) will move with an earthquake’s motion and can sustain extensive damage as a result. Base isolators work in a similar way like car suspension. It is not suitable for all types of structures and is designed for hard soil, not soft.
Types of Isolator
Lead-Rubber Bearin
Laminated steel-rubber isolators
Multi layer stones
Filled rubber bearings
Active base isolation
Other Types
Apart from bearing and sliding type, there are some other types of isolators, which are also used in building but rarely. Springs, rollers, sleeved piles are some examples of such isolators.
If you’re looking forward to a career that gives you the opportunity to build bridges, design tunnels and maintain and construct other infrastructure projects, then a career in civil engineering is an ideal career path to pursue.
The job of a civil engineer involves checking the site to make sure it is appropriate. There are many branches under this filed and each of them deals with different tasks, some of the branches are as follows:
Civil Engineering Fields:
Construction Engineering
Geo-technical Engineering
Environmental Engineering
Transportation Engineering
Structural Engineering
Coastal Engineering
Earthquake Engineering
Water Resource Engineering
Surveying
Municipal Engineering
Tunnel Engineering & more…
That’s because civil engineering jobs are all over the world. But it’s a good idea to know how much money civil engineers around the world earn on average to get a sense of what you can expect when negotiating a civil engineering salary. Here are some important factors to consider:
What Affects Your Civil Engineering Salary?
Several elements may impact your civil engineering salary including the location of your company, your level of education, your level of expertise and the amount of experience you have.
Salary based on experience
Salary Based On Level Of Education
For instance, civil engineers in the United States make an average annual salary of $65,189, according to PayScale. However, PayScale reports that civil engineers in Australia make an average of $73,051 AUD—about $50,798 USD—per year. Even the city, county, state or province where civil engineering jobs are may impact pay. For example, ZipRecruiter reports that civil engineers in Ontario, Canada make an average of $62,498 USD per year while civil engineers in Quebec bring in an annual salary of $77,011 USD.
Your experience may also impact how much you make as a civil engineer. For example, senior civil engineers in the United States make an average of $119,600, according to Glassdoor. But PayScale reports that senior civil engineers in Toronto, Canada, make an average of $100,964 CAD or about $76,697 USD. So, it’s worth considering the trajectory of your career path as a civil engineer.
The type of civil engineering role you hold also impacts how much you make. Some of the top three jobs for the highest civil engineering salary include engineering project managers, engineering managers, and senior civil engineers, making as much as $196,000 per year in the United States. Your industry may impact your pay, too. For instance, data from the May 2018 report from the U.S. Bureau of Labor Statistics reports civil engineers made the most working for the federal government excluding postal service jobs, bringing in a median annual salary $95,380.
You may also notice that different sources provide various ranges of salaries for civil engineering jobs. For instance, data from PayScale highlights that civil engineers in the United Arab Emirates (UAE) make an average annual salary of 74,604 AED or $20,311 USD. On the other hand, data from the Economic Research Institute (ERI) reports that civil engineers in the UAE make an average of 269,209 AED per year or $73,294 USD. This amount can also look different on a monthly basis. For instance, ZipRecruiter reports the U.S.-based civil engineers bring in an average of $6,418 per month. So, it’s a good idea to consult different sources to get an idea of how much to expect from your engineering salary.
What Do Salaries for Civil Engineering Jobs Look Like Around the World?
If you want a sense of what to expect from a civil engineering salary in a country you’re considering working in, it’s worth comparing salaries for civil engineering jobs around the world. Here are some common annual salaries for civil engineers worldwide, according to ERI:
The demand for civil engineers is bound to increase as the population increases. This is because of an increase in demand for infrastructures such as housing, highways, water supplies and sewerage. However, Civil engineering, like most fields, depends on the economy with the demand being high when the economy is doing well.
Prestressed concrete is adaptable to a wide variety of structural systems. These include pretensioned and post-tensioned structures, both cast-in-place and precast, and other prestressed elements in conjunction with normally reinforced concrete.
While there is no general classification for precast and prestressed concrete, it is useful to group certain elements and structures together to explain how prestressed and precast concrete is designed and constructed.
Prestressed and precast concrete may be considered in four broad categories:
Standardized Elements
Fixed Cross Section Elements
Fully Engineered Elements
Precast Nonprestressed Elements
While there is some overlap, each group has its own unique characteristics.
The role of the engineer varies with the type and complexity of the structural system being constructed. Indeed, multiple engineers may be involved in some aspect of the design, fabrication, and construction of the project. In general, the design engineer who is typically the licensed design professional or engineer of record is responsible for the overall design.
The unique characteristics of prestressed concrete often require the additional services of a specialty engineer. The specialty engineers can either provide consulting services to or be employed by a precast plant or contractor. Specialty engineers can also be associated with post-tensioning companies either as an employee or consultant.
In either case, the specialty engineer takes the concept prepared by the licensed design professional and prepares final detailed design calculations as well as developing fabrication or construction details necessary to complete the project.
Figure 1 : Typical standardized sections
Standardized Precast Prestressed Elements
Pretensioned concrete beams and slabs are typically constructed in reusable steel forms in a precast plant. Although a modest amount of custom formwork is used at precast plants, improved quality and reduced costs are realized only when standardized elements are used.
They consist of standard sections such as single-T and double-T beams, box girders, hollowcore slabs, inverted T-beams, and bridgegirders (Fig. 1). The capital investment required to construct and equip a precast plant includes the concrete mixing equipment, forms, stressing beds, curing systems, and heavy lifting equipment.
To obtain a return on this investment, the forms and stressing facilities must be in constant use. Efficiencies in production allow the precast pieces to be fabricated on a routine and daily basis.
The cost efficiencies of this type of fabrication allow architects and engineers to select the sections for a wide number of uses and be sure of availability and competitive cost. Hollowcore planks, single-T, and double-T beams are used for as floor elements in building construction, Figs. 2 and 3. Inverted-T beams support double-T and hollowcore elements.
These elements are commonly used in combination in office space, bridges, and parking garages, Fig. 4.
Figure 2 : Single-T floor beam before topping and cast-in-place beam
Figure 3 : Double-T floor element with suspended ceiling removed
Figure 4 : Precast concrete panel for parking garage
Standardized elements are creatively incorporated in building structures. For example, entire buildings have been constructed of double-T sections as is discussed in the commercial building case study. Double-T beams and box girders are used for short-span low-volume bridge girders.
For example, following the flood in the Big Thompson Canyon in Colorado, double-T bridges were installed to replace the original structures, Fig. 5. The double-T bridges allowed a standard design to be developed and installed in multiple locations in the canyon. This solution accelerated the reconstruction effort.
Figure 6 : Flat plate system with banded tendons
Figure 7 : Flat plate system with banded tendons
Engineer’s Role Standardized elements
The design engineer typically selects one of these standardized elements from references such as the PCI Design Handbook (2017) or the Manual for the Design of Hollow Core Sections (1998).
The design engineer may also contact precast plants located near the project to determine availability of sections.
The section type and the design loads are provided to the precast plant. Final detailed design engineering is completed by the precast plant or their specialty engineer in the form of shop drawings.
This process allows the design engineer the efficiency of selecting desired shapes for their function and allows the plant to select the appropriate number of strands, strand configurations, harping locations, and other details to maximize the performance of the plant operations to meet the project objectives.
Fixed Cross Section Elements
The design engineer is required to determine the prestressing forces and tendon locations in fixed cross section situations. Two common fixed section design conditions are post-tensioned beams and slabs for building or parking garage construction, and girders for bridge construction.
Other applications of fixed section elements include structures such as water tanks and post-tensioned slabs on-ground.
Flat plate and flat slab floor systems are ideally suited for the use of post-tensioning tendons, Figs. 6 and 7. Another popular system is one-way slab and beam floor systems that are cast-in-place, Figs. 8, 9, 10, and 11. The design engineer specifies a tendon profile geometry and an average effective post-tensioning force necessary to satisfy the design requirements.
The specialty engineer for the post-tensioning company then takes this requirement and produces a detailed design with tendon sizes and spacing along with anchorage and splice locations.
Pour strips and other detailing requirements necessary to isolate the post-tensioned element from other elements in the structure should be detailed by the engineer.
Selection of the tendon location is determined by the thickness of the slab. The maximum tendon eccentricity available to the engineer is determined by minimumcover requirements for corrosion and fire protection over the top and bottom of the tendon.
Therefore, in these applications, the section shape does not vary, but rather the design is controlled by the selection of the prestressed force and tendon spacing.
Another popular fixed section are two-way slab systems used as podium slabs.
Podium slabs are typically a single-story post-tensioned concrete floor system supported by columns that support a lighter superstructure above, which is usually wood or metal stud walls with a light floor system. These are popular for use in residential construction where the upper stories serve as the living areas and the area below the podium slab serves as parking. The podium slab is usually designed as a separate structure from that of the wood or metal stud superstructures. The individual structures may have two separate structural engineers.
Spliced bridge girders are an example of design to a fixed section using partially standardized precast, pretensioned elements that are also post-tensioned during the final stage of assembly, Fig. 12. State departments of transportation and AASHTO specify standard beam sections.
Precast plants have forms for bridge girder sections used in their market area. The section selection is dependent on the state practice and is further influenced by the distance that the girders are shipped. The variation and the magnitude of loads, load placement on the bridge, the girder spacing in the bridge, and the bridge deck design, preclude defining standard prestressing tendon forces and locations.
The design engineer selects from several choices regarding the layout and loading of the bridge prior to design of the prestressing force and location. Unlike standardized products, the design engineer specifies all details of the bridge girder.
Another example of spliced segmented precast construction using standardized shapes involves the use of plant-produced horizontally curved, precast concrete U-girders (Hamilton & Dolan, 2016). These U-girders use standardized shapes andgeometry along with post-tensioning to facilitate design and construction efficiency.
One example of this approach is shown in Fig. 13. Walls and tanks are a condition where the tendon location and force are determined within a fixed rectangular section, Fig. 14.
Figure 8 : One-way beam and slab system showing tendon passing through column at the top of the section and coiled slab tended ready to be placed
Figure 9 : One-way beam and slab system. Bundled tendons are seen at the beam bottom. Single slab tendons are on top of beam
Figure 10 : One-way slab and beam floor system. Slab tendons placed parallel with the slab span
Figure 11 : One-way beam end anchorage detail
Figure 12 : Spliced girder bridge
Figure 13 : Boggy Creek Road interchange at State Road 417 and Orlando International Airport’s
Figure 14 : Liquified Natural Gas tank showing circumferential post-tensioning tendons to ensure tank wall integrity under cryogenic conditions
Figure 15 : Parkland Hospital, Dallas, Texas. Seven stories are supported by girders with 62-ft cantilevers and 120-ft spans over an opening
Engineer’s Role with fixed section elements
The engineer’s role with fixed cross section element structures varies with the client and project. Some examples include:
Building design engineers specify the desired final prestress force. The contractor or post-tensioning company specialty engineer completes the design by determining the tendon spacing and stressing forces. The design engineer thenapproves the contractor’s shop drawing submittal.
Building design engineers specify the final prestress force, tendon location, and hardware detailing. Post-tensioning company engineer develops the tendon layout, anchorage location, and stressing sequence.
Bridge design engineers prepare the complete beam design, including detailed determination of prestress forces, tendon location, and construction sequence.
Projects such as tanks are often procured on a design–build basis. The contractor and either the contractor’s in-house engineering staff or a consulting engineer prepares the design to meet project requirements and the contractor’s preferred construction practice.
Fully Engineered Elements
Fully engineered elements require detailed engineering continuously during design and construction. Examples of fully engineered structures include segmental bridges, specialty transit structures, tanks, towers, stadiums, floating facilities, and unusual building construction. Design of these structures requires considerable engineering effort and often includes on-site inspection.
The complexity of these structures necessitates the engineer have a fundamental understanding of structural
behavior, loads, prestressing effects, and material behavior. Collaboration of efforts among engineers, precast plants, and general contractors is required.
Engineer’s role in fully engineered elements
Fully engineered elements require the engineer to define the loads, structural system, concrete section, prestressing
force, tendon location, and details (Figs. 15, 16, 17, and 18).
Figure 16 : Construction of Ironton Russell Bridge over the Ohio River. Longitudinal and transverse post-tensioning was used in the deck, which was cast-in-place using a form traveler.
Figure 17 : St. Anthony Falls Bridge over the Mississippi in Minneapolis.
Each bridge has a main span of 154 m that consists of precast concrete box girder segments supported by eight 21 m high piers. The end spans are 108 m longeach cast-in-place, post-tensioned concrete box girders built on false work which seamlessly blends into the precast main span sections
Precast Nonprestressed Elements
The major difference in grouping is that pretensioned elements require significant plant capitalization and stressing beds. Precast pieces can be fabricated on the jobsite or in a facility without stressing beds and other equipment associated with a plant operation. Tilt-up walls are an example of on-site precasting.
If a small amount of prestressing is required for delivery, erection or final loads, it is provided in the form of single-strand post-tensioned tendons.
Two examples of precast nonprestressed elements are architectural precast panels and tilt-up construction. Architectural precast panels can be used either as structural elements or the exterior finish of buildings, Figs. 1, 4, and 6.
The architectural panel finish can include color, texture, or simulated alternative materials such as a brick or stone (Fig. 19). Dyes or colorants are used in these special concrete mixtures.
The architectural surfaces are made in small quantities and placed only on the outermost one to 1–1/2 in. of the precast piece. The backing concrete would be normal concrete to reduce costs. Textures are fabricated by sandblasting, retardants that are power washed off, Fig. 19, or liners in the form to develop more complex surface features like Fig. 20.
Figure 18 : Woodrow Wilson Bridge replacement across the Potomac River near Washington, DC
Figure 19 : Architectural wall panel finishing
Figure 20 : Architectural panel finish simulating sandstone rock
Figure 21 : Tilt-up wall panel construction
Tilt-up construction is a specialized form of precast construction where wall elements are fabricated on-site in a horizontal position. The floor of the structure is cast first. Edge forms are then laid out on the floor and the floor surface becomes the bottom of the wall form.
The wall elements, complete with block-outs for windows and electrical or mechanical inserts, are then cast and allowed to cure in-situ.
After the concrete has cured, the entire wall panel is lifted into a vertical position (ACI 551.2R, 2015). The tilt-up panel is temporarily braced against wind loads, Fig. 21.
Connections between wall elements and roof elements provide stability. The roof diaphragm carries lateral loads to the end panels, which act as shear walls.
Tilt-up construction is commonly used for commercial structures such as warehouses, and industrial facilities. While some architectural finish is possible, the most economical tilt-up construction uses a plain or painted concrete finish. Tilt-up elements require two design considerations in addition to the design for vertical and lateral loads.
These conditions are determination of the lifting positions and associated lifting hardware and the temporary bracing systems. The temporary bracing prevents damage under wind loads and is designed for a 6 month return period rather than the full 50 or 100-year return period (ACI 551.1R, 2014; Shah, 1995).
Engineer’s Role Precast concrete
The design engineer is typically responsible for all design elements in precast pieces. The specialty engineer is responsible for the lifting details and temporary bracing as part of the construction effort.
What is 3D Concrete Printing? It’s advantages and disadvantages
Imagine a 3D print you get, of your dream home before the actual construction starts, wow that’s amazing! You can then even make the changes if you wish to or can even design the better ideas. Yes, 3D printing proving to be a revolutionary tool in this behemoth world of construction technology and management.
The construction industry in today’s scenario is known for its ability to adapt quickly or frequently the new innovative ideas that can raise the building sector. One the most innovations in this area are 3D printing. Let’s have a close look at what 3D printing is and how can it be beneficial in transforming into a lean, responsive sector.
3D printing these days is gaining more and more traction and has potential to ease some of the aches of the construction technology and management industry. 3D printing, which is the domain of engineering possibly, could make an extreme change in the ways that our building structures are built. Yes, the 3D printing technique is being looked like a must-have technology in the construction industry.
First a quick look on…
What 3D Printing Means?
3D printing is a production method of creating solid objects from a digital source uploaded to a 3D printer. The printer intelligently reads the files and lays down consecutive layers of materials such as plastic, resins, concrete, sand, metals until the entire object is created.
Unlike inkjet printers, a 3D printer has containers of raw material, like plastic which forces out the exact patterns to lay down layers.
Currently, 3D printers are only used to create 3D models of structural designs, various prototypes, landscaping bricks or decorative components. Uses of 3D Printers in Construction Technology and Management
3D printers are already in use in the construction industry. Gigantic 3D printers have already been built that can use solid materials to manufacture a variety of the major structural components, even the whole buildings.
Initially, printers can only extrude one type of equipment at a time, but now with the advent in the technology world, more advanced printers have been built that can extrude multiple materials providing a significant level of speed and resilience that was not before.
The printers may manufacture wall sections that can snap together like Lego’s, or they may print formative stage that can be latterly filled to create a full-size wall. The printer can be shifted to a construction site to manufacture on demand.
Benefits of 3D Printing in Construction
The 3D printing benefits include:
Consumption of material is optimized.
Increases the ability to design a larger variety of customized homes and buildings.
The construction waste is saved.
Huge save in labour cost
Growth in productivity.
Faster construction.
Quality can be maintained.
Some disadvantages of 3D printing include:
Reduced employee number in theconstruction industryas the machine does most of the work.
A finite number of materials can be used since the printer cannot be able to print the required design in various materials.
Transportation of printers on job site becomes risky.
Any errors occur in a digital model can result in an uncertain situation on site during the printing or construction phase.
Bearings are mechanical systems which transmit loads from the superstructure to the substructure. In a way, bearings can be thought of as the interface between the superstructure and the substructure.
Their principal functions are as follows:
1.To transmit loads from the superstructure to the substructure, and
2.To accommodate relative movements between the superstructure and
the substructure.
Types of Bearings:
Bearings may be classified in two categories:
1.Fixed bearings (allow rotations only)
2.Expansion bearings (allow both rotational and translational movements)
Following are the principal types of bearings currently in use:
1.Sliding Bearings
2.Rocker and Pin Bearings
3.Roller Bearings
4.Elastomeric Bearings
5.Curved Bearings
6.Pot Bearings
7.Disk Bearings
Pot Bearings
A pot bearing comprises a plain elastomeric disk that is confined in a shallow steel ring, or pot. Vertical loads are transmitted through a steel piston that fits closely to the steel ring (pot wall).
Translational movements are restrained in a pure pot bearing, and the gravity loads are transmitted through the steel piston moving against the pot wall. To accommodate translational movement, a PTFE sliding surface must be used. Keeper plates are often used to keep the superstructure moving in one direction.
Types of Pot Bearings
In general, the movement accommodated by fixed and expansion bearings can be classified by the following:
Fixed bearings allow for rotation only
Guided expansion bearings allow for rotation and longitudinal translation only
Multi-directional expansion bearings (sliding bearings) allow for rotation and translation in any direction
Figure 1 : Types of Por Bearings
Fixed Pot-Bearings
A non-reinforced elastomer is placed between a precisely milled steel pot and a cylindrical lid.
Vertical loads are transmitted through a steel piston that fits closely to the steel pot wall. Flat sealing rings are used to contain the elastomer inside the pot. The elastomer behaves like a viscous fluid within the pot as the bearing rotates. Because the elastomeric pad is confined, much larger load can be carried this way than through conventional elastomeric pads.
Figure 2 : Fixed Pot-Bearings
Guided Pot-Bearings
A Uniaxial Displaceable Pot Bearing (Guided Pot Bearing) releases the lateral movements of bridge in any one direction utilizing a guide on the lid and a guiding groove in the gliding plate.
The gliding ability is accomplished by the embedded PTFE (Teflon®) disc and the gliding austenitic steel, which is welded onto the bottom of the gliding plate.
Figure 3 : Guided Pot-Bearings
Sliding Pot-Bearings
The Multiaxial Displaceable Pot Bearing (Sliding Pot Bearings) releases lateral movements of the bridge in all directions.
The gliding ability is accomplished by the embedded PTFE (Teflon®) disc and the gliding austenitic steel, which is welded onto the bottom of the gliding plate.
Figure 4 : Slidin Pot-Bearings
Components of Pot-Bearing
Figure 5 : Components of Pot-Bearing (Fixed Pot-Bearing)
Figure 6 : Components of Pot-Bearing (Guided Pot-Bearing)
Bearing Schedule
First, the vertical and horizontal loads, the rotational and translational movements from all sources including dead and live loads, wind loads, earthquake loads, creep and shrinkage, prestress, thermal and construction tolerances need to be calculated. Then, the table below may be used to tabulate these requirements.
Shrinkage cracks in concrete occur when excess water evaporates out of the hardened concrete, reducing the volume of the concrete.
CREEP:
Deformation of structure under sustained load. It’s a time dependent phenomenon. This deformation usually occurs in the direction the force is being applied. Like a concrete column getting more compressed, or a beam bending.
Creep does not necessarily cause concrete to fail or break apart. Creep is factored in when concrete structures are designed.
SHRINKAGE EFFECTS:
The shrinkage of the prestressed beam is different from the shrinkage of the deck slab.
This is due to the difference in age beam and slab therefore the differential shrinkage induce stresses in prestress composite beams.
Larger shrinkage of deck causes composite beams to sag.
DIFFERENTIAL SHRINKAGE :
Differential shrinkage between Slab and PS Beams creates internal stresses. It is assumed that half the total shrinkage of the beam has taken before the slab is cast.
The effect of differential shrinkage will be reduce by creep. Allowance is made for this in the calculation by using creep coefficient φ.
Eccentricity = y top of composite section – half of slab thicknes
CALCULATION OF INTERNAL STRESSES
Restrained Stress (RS) = έDS x Ec x Ф
Axial Release (AR) = RF / X-sec area
Moment Release (MR) = RM x y / inertia
(for top and bottom stresses)
NET STRESSES:
TOP STRESSES:
Σ(RS , AR , MR)
BOTTOM STRESSES:
Σ(MR , AR)
CREEP EFFECTS:
We know creep are deformation under the sustained load as in case of prestressed beams prestressing load is applied at the bottom cause the deformation in upward direction and due to creep effect as time passes through long term deflections in upward direction is increases.
For camber calculation longterm deflection factors
Dead = 2.0, SDL = 2.3, Prestressing = 2.2
This increase in upward direction of simple span beam is not accompanied by stress in beam since there is no rotational restraint of the beam ends.
When simple span beam are made continuous through connection at intermediate support, the rotation at the end of the beam tend the creep to induce the stresses.
Types of Dams, advantages, disadvantages and classification
What is a Dam?
A dam is a structure built across a stream, river or estuary to retain water. Dams are made from a variety of materials such as rock, steel and wood.
Structure of Dams:
Fig 1 : Structure of Dams
Definitions:
Heel: contact with the ground on the upstream side
Toe: contact on the downstream side
Abutment: Sides of the valley on which the structure of the dam rest.
Galleries: small rooms like structure left within the dam for checking operations.
Spillways: It is the arrangement near the top to release the excess water of the reservoir to downstream side
Sluice way: An opening in the dam near the ground level, which is used to
clear the silt accumulation in the reservoir side.
Advantages of Dams:
Dams gather drinking water for people -> Water Supply
Dams help farmers bring water to their farms -> Irrigation
Dams help create power and electricity from water -> Hydroelectric
Dams keep areas from flooding -> Flood Control
Dams create lakes for people to swim in and sail on -> Recreation &Navigation
Disadvantages of Dam
Dams detract from natural settings, ruin nature’s work
Dams have inundated the spawning grounds of fish
Dams have inhibited the seasonal migration of fish
Dams have endangered some species of fish
Dams may have inundated the potential for archaeological findings
Reservoirs can foster diseases if not properly maintained
Reservoir water can evaporate significantly
Some researchers believe that reservoirs can cause earthquakes.
Classification of Dams
Classification based on function
Storage Dam
Detention Dam
Diversion Dam
Coffer Dam
Debris Dam
Classification based on hydraulic design
Overflow Dam/Overfall Dam
Non-Overflow Dam
Classification based on material of construction
Rigid Dam
Non Rigid Dam
Classification based on structural behavior
Gravity Dam
Arch Dam
Buttress Dam
Embankment Dam
Rock-fill dam
1 – Gravity dams
Gravity dams are dams which resist the horizontal thrust of the water entirely by their own weight.
Concrete gravity dams are typically used to block streams through narrow gorges.
Material of Construction:
Concrete, Rubber Masonry
Fig 2 : Example of Gravity Dam Design
Fig 3 : The Grande Dixence Dam in 2004, facing west and Mont Blava (Source Wikipidea)
2- Arch Dam
An arch dam is a curved dam which is dependent upon arch action for its strength.
Arch dams are thinner and therefore require less material than any other type of dam.
Arch dams are good for sites that are narrow and have strong abutments.
Fig 4 : Jinping-I Dam also known as the Jinping-I Hydropower Station or Jinping 1st Cascade
Buttress dams are dams in which the face is held up by a series of supports.
Buttress dams can take many forms – the face may be flat or curved.
Material of Construction: Concrete, Timber, Steel
Embankment dams are massive dams made of earth or rock.
They rely on their weight to resist the flow of water.
Material of Construction: Earth, Rock
Fig 8: Embankment Dam Design
Fig 9 : Cross-sectional view of a typical earthen embankment dam
5- Rock-fill dam
These types of dams are made out of rocks and gravel and constructed so that water cannot leak from the upper stream side and through the middle of the structure. It is best suited in the area where rocks are around.
Fig 10 : Mohale Dam, Lesotho: highest concrete-face rock-fill dam in Africa
