Concrete Joints, Tilt-Up Construction, Formwork, and Cladding

Posted on Mar 18, 2025 in Hotel Administration and Management

Concrete Joints

Q1. The magnitude of most concrete floor construction is such that interruptions will inevitably occur in the placing of concrete, in which case a joint must be formed. Sketch and explain the construction and function/purpose of the following types of joints found in concrete:

a) Construction Joints

The aim of a construction joint is to make the joint as strong as possible. Construction joints occur where two successive placements of concrete meet. They are frequently found in footings, columns, beams, and slabs. In slabs, they may be designed to permit movement and/or to transfer load. Careful pre-planning of the placement is important for minimum crack-free structural members. Construction joints “key” the two edges of the slab together to provide transfer of loads, to help prevent curling or warping of the two adjacent edges, or uplift from its neighboring poured slab, keeping the various poured slabs locked together as one unit, thus allowing zero movement either side of the joint.

Construction joint placed in SOG:

b) Isolation Joints

Isolation joints allow movement in both vertical and horizontal directions. They allow for drying shrinkage and other movements to occur between a concrete slab without damaging adjacent structures, such as columns, walls, footings, and other points of restraint such as machine foundations and stairwells.

The gap is filled using a pliable filler, such as a floating floor-to-column isolation joint:

Control and Contraction Joints

Q2. Explain the difference between a Control (Dummy) Joint and a Contraction Joint:

a) Control (Dummy) Joint

A control joint is a continuous vertical joint filled with mortar, but with a bond breaker on one side so that tensile stress cannot develop across the joint. If control joints are not provided, a concrete masonry wall may crack as it shrinks over time. Control joints weaken the concrete by creating a groove at selected points (joint position) where the crack is likely to occur due to shrinkage (often the middle of the slab).

b) Contraction Joint

Contraction joints are deliberately “placed” in the fresh concrete before it has a chance to create its own joints, i.e., cracks. What a contraction joint really is, is a deliberate crack in the slab that is forced to follow a line of our own choosing.

Contraction joints are formed by saw cutting, by tooling a joint with a grooving tool, or by inserting a plastic strip into the concrete during finishing (zip-strip). Proper timing and depth of cut are essential. If you wait too long, the slab will crack where it wants to rather than where you want it to. And if the joint is not cut deep enough, it will not create the plane of weakness needed to guide the crack.

Tilt-Up Construction

Q3. Tilt-up cast-on-site 150mm thick wall panels have revolutionized the construction of commercial low-rise buildings, such as factories and shopping centers. Briefly describe five (5) advantages of Tilt-up construction over normal/traditional techniques of concrete construction (i.e., in-situ reinforced concrete):

Tilt-up is a form of construction ideally suited to the rapid realization of a wide range of buildings for industrial, commercial, residential, and community use. It provides the benefits of solid concrete-walled buildings quickly and economically.

1. Cost: Tilt-up construction is highly competitive with traditional construction over a wide range of building types and sizes – e.g.: warehouses, churches, residential houses, hotels, and restaurants.
2. Energy Conservation: Air penetration is minimized. Can be economically insulated to whatever insulation values are required, from a normal building through to highly insulated cold stores.
3. Durability: The strength of concrete coupled with the uncomplicated method of construction offers reliable durability.
4. Fire Resistant: Concrete has a good ability of fire resistance – designed for up to four hours of fire resistance. Particularly cost-effective as fire separation and compartment walls.
5. Safety: As most of the work is completed at ground level, there is no vertical formwork or scaffolding. Due to the floor slab being poured first, workers have a safer working surface, resulting in potential accidents.

Precast vs. Tilt-Up Panels

Q4. What is the difference between “precast panels” and “tilt-up panels”?

The main difference between tilt-up construction and precast construction is the location where the concrete panels are formed. Precast is fabricated outside and transported to the site, tilt-up panels are poured on site.

• Tilt-up panels: Poured on the job site using a casting bed, and then lifted into place using cranes. Forming the panels on site eliminates the need for transportation, but since the panels are poured and cured outside, weather conditions need to be taken into consideration.
• Precast concrete: Panels are formed off-site, usually in a factory.

Stack Casting vs. Single Casting

Q5. In Tilt-up construction, what is meant by “stack casting” and “single casting”? In what situation would they be used?

• Stack casting: Due to job site area restrictions, “stack casting” panels on top of each other is a common method used on site to free up space. Quite often a separate casting pad is poured for this purpose and is removed when the panels are erected. Cranes are used to tilt the concrete elements from the casting slab to a vertical position.
• Single casting: Completed when adequate floor area is provided, which allows for easy set-out of patterns in wall and panels.

Weather-Resistant Panel Joints

Q6. List the main types of weather-resistant panel joints:

One-stage joint, multi-stage joint, dry baffle joint.

Mobile Crane Selection

Q7. Explain, in bullet form, the factors to be considered when selecting a mobile crane (capacity) to lift and position tilt-up panels:

• The lifting capacity of the crane (height, reach, and load capacity).
• The crane’s capacity influences the number of set-up positions needed for lifting all the panels.
• Panels are transported to the site, often need to be rotated through 90° so that they hang vertically. The crane will need to have sufficient capacity to be able to carry the panel on each of the two cables to accomplish this rotation.
• Rotation has to be accomplished without fouling existing construction, panels, or bracing.

Strongback Function

Q8. With the aid of a sketch (and words) explain what the function of a ‘strongback’ is?

Strongbacks are used to support oddly shaped or elongated panels with large or unhandy located openings, while lifting.

Tilt-Up Construction Safety

Q9. List six (6) safety considerations that should be noted when using the Tilt-up construction system:

1. Before lifting starts, hold a safety meeting. Ensure all workers on the job have been well informed of the lift process, create a safety checklist and have workers sign.
2. Ensure that the foreman and the crane operator know all the hand signals they will use to communicate with each other throughout the lift process.
3. Don’t lift panels during high winds.
4. Do not use damaged or bent braces, lifting hardware, or bolts.
5. Maintain a daily torque log on brace insert tightening.
6. Never release the crane load if the bracing does not appear adequate.

Tilt-Up Wall Panel Components

Q10. The following sketch shows a cast ‘Tilt-up’ wall panel formed and poured on top of the ground slab. Label the components indicated.

Bond Breaker Purpose

Q11. In tilt-up construction, what is the purpose of the bond breaker between panels?

A bond breaker is a substance applied to concrete surfaces to ensure that there is *no* permanent bonding between the surfaces. Bond breakers are used normally on tilt-up walls and precast segments to ensure the right pieces are *not* cast together. Bond breakers will allow lifting and moving of precast pieces after stripping them from the form.

Formwork Surface Finish Classes

Q12. AS 3610 – Formwork for concrete defines several classes of surface finish of formed and stripped concrete surface. 5 Classes:

1. Class 1: Best finish, of the highest standard. Suitable for elements contained in a single pour. Recommended for use in very special features of buildings of a monumental nature.
2. Class 2: High-quality finish requiring substantial input by the designer. Covers most good quality architectural precast.
3. Class 3: Acceptable standard for many industrial and civil structures, resulting in cost savings for the owner.
4. Class 4 & 5: Visual quality not of importance. Surface usually concealed from general view/never seen, i.e. footings and slabs.

Lost Formwork Product

Q13. Name a product that can be used as “lost” formwork.

Bondek or Condek. It is a lightweight metal product that can be ordered to specific lengths. It can be used in situations where stripping cannot be done once the concrete has been poured.

Formwork Consultation Items

Q14. According to the “Code of Practice for Formwork” consultation between builder, formwork contractor and structural engineer (when appropriate) is required during erecting and dismantling of formwork and associated equipment. List six (6) items that should be considered during the consultation process.

1. Nature of the work.
2. The type of form to be used.
3. The height of the formwork to be erected.
4. The size of the formwork deck.
5. Availability of equipment.
6. Public safety.

Engineer’s Certificate Exceptions

Q15. According to AS 3610, the adequacy of the components of the formwork for a suspended slab or beam must be inspected & certified by an engineer prior to pouring of the concrete. List two (2) situations when this certificate is not required.

Slab on ground construction (no reinforcing requirement) e.g. footpath, kerb and gutter.

Project Documentation Items

Q16. Project documentation must be provided for any matters associated with the formwork construction, concrete placement or formwork removal, which are critical to the serviceability of the permanent structure.

a) List four (4) items that should be specified or indicated in the project documentation in addition to the description of the concrete element:

1. Steel specification and size.
2. Concrete finish class (1-5).
3. Strength of concrete (MPa).
4. Tensioning requirement.

b) Explain what is meant by class of finish in relation to formwork and name the document that defines these classes of finish:

AS 3610- Formwork for concrete, TABLE 3.2.1

Suspended Slab Formwork Members

Q17. Name members shown in the sketch below of a standard suspended slab formwork system:

Structural Frame Stabilization

Q19. Apart from diagonal and cross bracing, how else can the structural frames be stabilized/braced?

Knee bracing / Gusset bracing / Haunch.

Portal Frame Definition and Types

Q20. Define a portal frame, and with the aid of labelled sketches briefly describe the two (2) types of portal frame systems that exist (Sketches need only be of single line with notification):

Portal frame: Usually made from steel, but can also be made from concrete or timber. Most common form of enclosure for spans of 20-60m. They are two-dimensional rigid frames designed to reduce bending movement in the beam, allowing the frame to act as one structural unit. Generally used for single-story construction which require a large unobstructed floor space. Often used in factories, shopping centers and warehouses, such as Bunnings.

1. Pitched roof portal frame

2. Portal frame with internal mezzanine – Office accommodation is often provided within a portal frame structure using a partial width mezzanine floor

Steel Portal Frame Knee Joint Construction

Q21. Sketch two (2) different ways/methods of constructing the rigid “knee joint” of a steel portal frame:

Tapered haunch:

Curved haunch:

Haunch Use in Steel Portal Frames

Q22. Why is a “haunch” often used in steel portal frame construction?

To make the connection deeper than the main rafter section for additional stiffness.

Portal Frame vs. Post and Lintel

Q23. Portal Frames are often used to span large comparative distances as opposed to column and beam (post and lintel) construction. Give one advantage and one disadvantage of “Portal Frame” system over the “Post and Lintel system”:

Advantage: Cheap, quick, and fire-resistant.

Disadvantage: Time, takes extra formwork, concrete pour.

Braced Bay Components

Q24. The sketch below shows the structural components in a “braced bay” of a portal frame structure:

Rigid vs. Flexible Base Connections

Q25. Which of the following “base connections” is a “rigid” one and which one is a “flexible” one. Explain why?

Rigid: Designed to resist moments or rotation within the joint (fully welded steel joint, reinforced concrete joint, glue laminated joint).

Flexible/pinned/hinged: Considerable or complete rotation can occur within the joint (single and double bolted connections, skew nailing).

Fly Bracing Function

Q26. Explain the function of “fly bracing”:

Reduce span, support, direction of wind loads, prevent a column or rafter from twisting or rotating when under load.

Bolted Site Connection Popularity

Q27. List 4 reasons for the popularity of bolted site connections:

1. Low sensitivity to unavoidable dimensional inaccuracies in fabrication or shop detailing.
2. Simplicity and speed of installation.
3. Low demand on skills of workers.
4. Relatively light and portable tools.

Bolt Categories

Q28. What are the 2 most common categories of bolts?

Grade 4.6 and grade 8.8 – FRICTION AND BEARING.

Bolt Type 4.6/S Meaning

Q29. Explain what each figure and letter mean in bolt type 4.6/S:

• Strength grade: 4.6
• S: SNUG FIT
• Min Tensile Strength (MPa): 400
• Min Yield Strength (MPa): 240
• Name: Commercial
• Australian Standard: AS 1111

8.8/TF vs. 8.8/TB Bolts

Q30. What is the difference between 8.8/TF and 8.8/TB bolts?

• 8.8/TF: High Strength Structural Bolt – Fully Tensioned Friction Type Joint.
• 8.8/TB: High Strength Structural Bolt – Fully Tensioned Bearing Type Joint.

HS Structural Bolt Tightening Methods

Q31. What are the 3 methods of tightening HS Structural Bolts?

• Part-turn method.
• Torque control method.
• Load indicator method.

Bolted Connection Failure Types

Q32. List the types of failure in bolted connections:

• Fracture across the connected element.
• Bearing failure at bolt interface (elongation failure).
• Tearing failure (too many holes may cause tearing of metal between plates).
• Shearing.
• Over tightening.

Welded Connection Advantages and Disadvantages

Q33. List 2 advantages and 2 disadvantages of welded connections:

Advantages: Fast, saving in material.

Disadvantages: Need skilled labor, may not have proper equipment on site, can be dangerous – sparks.

Welded Connection Symbols

Q34. Name/explain the following symbols used in welded connections:

Fillet Location – Arrow side / Weld All Around / Field or Site Weld

Welding Categories

Q35. List and briefly explain/describe the 2 welding categories:

• Category SP: (Structural Purpose) intended to be used for relatively highly stressed welds statically and dynamically loaded joints – mostly butt welds.
• Category GP: (General Purpose) statically loaded joints – most fillet weld low-stressed and non-structural welds.

Fillet Weld Uses

Q36. What are the 3 main uses of fillet welds?

For lap splices, for T-joints, for corner joints similar to T-joints.

Wall Cladding Functional Requirements

Q37. Cladding is a form of masking or infilling a structural frame

a) List and briefly describe 4 primary functional requirements that any form of cladding has to satisfy:

Custom, corrugated, pre-cast, Hebel, sandwich panel – insulation in-between

1. Be self-supporting between the framing members – i.e. constructed to a suitable size.
2. Resistance to water penetration – cladding must prevent the entry of water, e.g. rain, snow and ice into building.
3. Provide thermal efficiency.
4. Resistance to air leakage (wind penetration) – prevent the unintended passage of air between indoors and outdoors.
5. Resistance to both positive and negative wind pressures.

b) Some of the materials used for external wall cladding are GRP and GRC. What do these abbreviations stand for and where are they commonly used?

• GRP: Glass Reinforced Polyester (plastic), e.g. water tanks, roofing, lightweight cladding panels.
• GRC: Glass Reinforced Concrete, e.g. architectural façade, cladding panels.

c) Define and briefly describe “Curtain Walling” in relation to external wall cladding?

Aluminium-framed wall containing in-fills of glass panels, usually double-glazed. Often seen across commercial buildings, high-rise buildings and museums. External lightweight cladding attached to a framed structure forming a complete envelop or sheath around the structure able to withstand the elements such as loads, winds and fire. Non-load bearing wall. The framing is a self-load that gets attached to the building structure and does not carry the floor or roof loads of the building.

d) List 6 functions/performance requirements that any form of cladding has to satisfy:

1. Keep environmental elements out.
2. Provide thermal efficiency.
3. Provide acoustic efficiency (air-born and impact).
4. Control lighting.
5. Self-supporting between members.
6. Architectural design – aesthetics.

e) List 4 external wall cladding systems used for commercial institutional or residential buildings (not domestic):

1. Panel walls with or without attached facings.
2. Concrete and similar cladding panels.
3. Light infill panels.
4. Curtain walling.
5. Brickwork.
6. Hebel.
7. Precast.
8. Tilt-up.
9. Sandwich panels – metal clad on both sides and insulation in-between.