Harmony & Concord Blocks

The Most Common Building Design in Hong Kong

Harmony Block projects from the Housing Authority are usually composed of 3 identical blocks plus some open space facilities etc. This arrangement is considered to be optimum. This photo series is based on a case study of Phase IV redevelopment at Lam Tin Estate.

The ground and first floor in Harmony Block are non-typical. The slab of the first floor is often designed as a transfer plate, which is heavily reinforced especially in the main beams. The ground floor frequently has more headroom. The formwork employed in these floors is mainly panel-type form using plywood and timber. It usually takes around three months time to complete the ground and first floor.

With the ground floor completed and the slab of first floor still under temporary support, the steel reinforcement fixing for the first floor wall is almost completed. Timber forms will then be erected after the steel is inspected by an engineer. Note the special formwork used on the in situ reinforced concrete facade on the external wall. The facade for the upper floors is constructed using precast units instead of forming by in situ method.

A closer look at the special formwork system used on the first floor facade. This formwork is made of aluminium alloys, a pioneering material for this type of housing project. However, as the complicated jointing treatment between the facade and the internal walls caused serious construction delays, this pilot set-up was seldom seen afterwards.

The precast facade unit for a typical floor has been temporarily erected on the slab. The facade will be later enclosed by an internal wall form and will provide a structurally rigid and watertight joint between the external and the internal walls after concreting.

Foundation and substructure design for a typical Harmony Block project is simple. H-piles, precast concrete piles or sometimes medium to small diameter in situ concrete piles are the common foundation choices. Basements are seldom used in the Harmony Block design. The substructure mainly consists of the required pile caps, ground columns and ground beams.

A worker erects the aluminium form for the first floor facade. One of the drawbacks of this formwork system is that it uses many small components and accessories to allow the formwork be erected manually. This is very time-consuming and inappropriate for site fabrication.

This junctioning detail shows the connection between the precast facade and the wall form before concreting.

The steel form for the internal walls is positioned and ready for the concreting process.

In addition to the access platform mounted on the steel form of the internal walls, the steel form for the external walls has a two-level scaffold attached on the lower side. This allows access to the outer face of the form on the upper level, as well access for touch-up works on the fresh concrete surfaces at the lower level.

A high-level view shows the most complicated part of the Harmony Block construction: the common core for the lift shafts and staircases. Note the special box-shaped steel forms (six in number) used to form the lift shafts. The staircases (one with the formwork still on, while the other has had the formwork removed) can be seen on the two corners.

Precast concrete panels (often known as semi-slabs or sub-slabs) are placed on top of the internal walls and act as permanent shutters for the floor slab. After the sub-slab has been positioned and levelled, reinforcing bars will be erected. After placement of the concrete, it becomes the structural slab of the floor.

The layout of the completed formwork for a typical wing. The concreting process will be carried out in the forthcoming cycle.

The staircase shaft: Precast stairs will be erected into the shaft to form the completed staircase. The workers inside the shaft are forming a chase using hand chisels for the future connection of the reinforced concrete landing. The steel link bars, already in place in the concrete wall, will be recovered. The landing for the staircase will be constructed in situ later.

A panoramic view demonstrates a typical cycle in the construction of the Harmony block. A typical floor is divided into five sequential phases: the common core and the four wings. Starting from the top wing in a anti-clockwise direction, we first see the slab just being concreted in the top wing and being prepared for the wall steel fixing. In the left wing, the sub-slab has been positioned and the floor reinforcing bars have been erected prior to the concreting work in the forthcoming stage. The lower wing is just having the wall concreted, and the wall form will be removed for erection in the right wing.

The box-shaped steel forms. This formwork is operated by a lever system, and can be easily placed or removed by the tower crane.

The overall view of the onsite precasting yard.

Looking into the staircase shaft: One precast stair flight together with the cast-in situ landing have already been placed, while the supporting provision (corbel and dowel bars) for the next flight has also been prepared.

The stacking area for the precast units. These units will soon be put into a curing chamber before they are strong enough for actual use.

The steel mould for the fabrication of the precast facade. In the photo, workers are placing concrete into the mould for the casting of the unit.

Layout arrangement for one of the two onsite curing chambers. Four steel panels form the walls, topped by a steel cover. Freshly cast units are placed in the chamber overnight and cured by steam; The moist heat of steam improves the strength of the concrete. The three tower blocks onsite consume quite a few of these units, so the production rate of the units is matched to the consumption rate.

The steel form used to form the staircase, as viewed from the exterior.

Several precast facades on the ground, ready to be lifted to the upper floors for erection. The fixing blankets on the side of the units and the projected eave at the bottom can clearly be seen in the photo.

In the older system, a precast facade was fixed to the external wall position at a later time after the casting of the upper few floors. The one seen in this photo is having the lower floors with the facade erected, while the upper two floors await the fixing of the facade.

The Harmony blocks are of shear wall design. The blocks shown in this photo, with only the lower floors cladded with the precast facade, best illustrate the structural arrangement of the building.

The latest generation of public housing - the Concord blocks - were introduced in 1997 and boast two improved features. From the architectural point of view, Concord has a more spacious design and has eight flats on a typical floor, providing greater privacy than the 16 to 18 found on the typical Harmony block floor. From the construction point of view, the Concord block is designed to facilitate the use of a more streamlined formwork system in the production process. The one in this photo is a typical project of this type in the Fanling area at its beginning stage, composing of four identical 40-storey blocks and using a formwork system called 'Jump Form.'

Close up of the formwork arrangement of a Concord block. The ground floor is a non-typical floor and is constructed using timber form. From the first floor onwards, the 'Jump Form' will be used to construct the entire building.

Similar to other mechanised formwork systems, the setting up of the form requires a long set-up period before full operation. In this project, it took two months. Since the form for the common core is simpler and smaller, it rises much quicker than the wings at the early stages. The difference of 4-5 storeys, shown in this photo, is near the limits of tolerance.

The 'Jump Form' lifting action is performed by screw-action-operated jack rods powered by an electric motor with a gear box set. The wall forms are composed of large steel shutter panels which can be easily positioned or removed by track rail, and which are mounted on supporting joist frames articulated to the jack rods. This photo shows one of the wall shutters being hung on the track rail ready for placement.

Detail showing how the wings are joined to
the common core.