Assembling process

In general, an efficient assembly process can be achieved by two persons for the short 2.3 m beams, but four people are needed for the long 4.8 m beams. The author was able to do much of the machining and manufacturing with assistance as needed. In this way it was possible to have a direct control of the quality of the work and also to evaluate different profiles in terms of the cost and workmanship required in fabricating the various beams.

Assembling processes are summarized in the following steps:

• Preparing the glue

• Preparing the components

• Applying the glue

• Initial assembling

• Clamping the beam

• Releasing the clamp and transferring the beam to the curing place Preparing the Glue

Adhesive was mixed with liquid hardener using a ratio of 100g adhesive to 33g liquid hardener.

CHAPTER 3:MANUFACTURING AND FABRICATION PROCEDURES

3.3.3.1 Double I-Beams and LVL Double I-Beam

There follows a description of the assembly process for Double I-Beams and LVL Double I-Beams. This was the initial manufacture process for any of the beams and the assembly pattern described is repeated for other designs.

Glue was brushed within the flange slots and also brushed in the tapered area and tongue and groove surface of the plywood webs as shown in Figures 3.9(a), 3.9(b) and 3.9(c). The plywood webs were tapped into one slot and then into the second slot.

Then the second flange was adjusted onto these two webs. In order to get the webs into the top flange, both flanges were tapped with a plastic hammer. First the webs were adjusted in the top and bottom flanges, then the connection between the tongue and groove joints was checked. If there was a gap, it was closed by tapping the webs from both ends. When the adjusting was completed the top flange was hit with a rubber hammer so that the flange was tight enough for transferring to the clamp: see Figure 3.9(d).

(a) Applying the glue to the grooving area (b) Adjusting the webs within the grooved area

(c) Applying the glue to the webs (d) Adjusting the top flange

Figure 3.9 Fabricating the Double I-beam

CHAPTER 3:MANUFACTURING AND FABRICATION PROCEDURES

The beam was placed between two lengths of LVL, serving as packers, in the Taylor-clamp. These LVL packers help to distribute the clamp pressure evenly over the beam flanges: see Figure 3.10. Discussions with SCION Research staff led to the conclusion that a pressure of 60 Psi (41 kN/m²) would be adequate for obtaining a good bond between the webs and flanges.

Figure 3.10 Pneumatic press clamp (Taylor clamp)

A similar procedure was followed for assembling the long Double I-beam, but instead of a Taylor clamp a modified Glulam clamp was used as shown in Figure 3.11.

Clamping in this way proved to be difficult and labour intensive. There is a possibility of web debonding when the beam is transferred to the clamp or when it is adjusted within a clamp.

CHAPTER 3:MANUFACTURING AND FABRICATION PROCEDURES

Figure 3.11 Clamping system used for long I-beams and Double I-beams

Unlike Box beams, Boxed I beams and Box Double I-beams, there is no need for the long double-I beam to remain in the clamp for number of hours. This is because of the self-clamping characteristics of tongue and groove profiles. Once the web is pressed in its groove then immediately the assembly can be removed from the clamp.

3.3.3.2 Box Beam

This design is the typical box beam although without a stiffener. Glue was applied on the flanges by a roll-spreader. Glue was also applied on the connection area of the plywood and brushed in the web’s tongue and groove area. Then the web was placed on the flanges and fixed by a brad-nailer. The second web was placed next to the first web connected to each other by tongue and groove joints. The same procedure was repeated for the other side of the beam and then the assembled beam was transferred to the clamp as shown in Figures 3.12 and 3.13.

Load cell

CHAPTER 3:MANUFACTURING AND FABRICATION PROCEDURES

a)Box beam under the clamp b) Torque wrench and load cell for controlling the clamp pressure

Figure 3.12.Laminated press for short Boxed profiles

(a) Fabrication of long span Boxed beam (b) Using insulated covers and gas-fired heating for curing the beams

Figure 3.13 Modified Glulam press had been used for fabrication of the Boxed beams

3.3.3.3 Boxed I-Beams

Adhesive was prepared as explained previously. In this design the total mixing time, open assembly, close assembly and clamping time should not exceed 30 minutes when the temperature is 18^oC or above. If the process takes longer then the glue will be too dry before clamping and the bond between web and flange will be poor. By measuring the required time for assembling the short 2.4 m beam and the long 4.8 m beam, it was established that it is possible to assemble 3 beams inside 30 minutes

CHAPTER 3:MANUFACTURING AND FABRICATION PROCEDURES

provided two people work with the 2.4 meter beam and four persons work with the 4.8 meter beam.

Manufacturing the Boxed I-beam took place in two stages:

Stage 1

The middle web was glued in place. Adhesive was brushed within the slot of bottom and top flanges. Glue was also applied on the tapered part of the web and on the tongue and groove area of the plywood web. Plywood webs were adjusted in the bottom flange one by one and then the top flange grooving was fixed to the plywood web. The plywood tongue and groove joint was controlled and any gap between them, was adjusted by tapping the other end of the plywood webs. The upper flange was hit with a rubber hammer and then the beam was carried to the clamp. The clamping procedure is similar to that for profiles 3 and 4, but only 50 PSI pressure was applied.

Stage 2

Glue was prepared in the same fashion explained before, and then it was applied on one side of flanges and the webs by roll-spreader. After adjusting the plywood webs on one side the web is fixed in place using the brad-nailer and then the same procedure is repeated for the other side. The brad-nailer gun was used for holding the plywood webs in place before transferring to the lamination clamp as shown in Figures 3.12 and 3.13. Beams were placed between two packers of LVL 45mm deep, 300mm wide and 2400 mm long in order to even the pressure on the beams.

During each session four short beams were manufactured and then clamped for at least 7 hours. In order to reduce the curing time to 7 hours, a heating system was employed and the room temperature brought to 25-28^oC. Six beams were manufactured in two sessions per day. The second session had up to 17 hours curing time so there was no need to increase the temperature.

A similar procedure was followed for fabricating the long Box beam, but in each session three beams were assembled and a modified Glulam press was used for clamping as shown in Figure 3.13.

CHAPTER 3:MANUFACTURING AND FABRICATION PROCEDURES

3.3.3.4 Recessed Beams

Glue was brushed into the recessed area of the flanges. Glue was also applied on the web area, by roll-spreader. After webs were adjusted in their place the brad-nailer was used to hold the web against the flange. The same procedure was repeated for the other side of the beam. In this design before the final fixing by brad-nailer, a G-clamp was used to adjust the web in the recessed section, especially when the flange had some bending warp. In similar fashion to the assembly of the other design, the webs were joined together via their tongue and groove connections.

3.3.3.5 Boxed double I-beams

This profile is a combination of profiles 3 and 6. In the first stage the middle webs were adjusted in place as explained for profile 3 and than the side webs were glued in place.

Clamping pressure

First, all the 18 clamping bolts were closed by a pneumatic impact wrench and then tightened by a torque wrench. 60 N.m was the torque applied to the lamination clamp bolts. In order to have a better control on the clamping pressure, a load cell was used to check pressure, and it was attached within the middle clamp as shown in Figures 3.11 and 3.12. This load cell showed the actual load, which was carried by the clamp when the bolt was tightened by the torque wrench. This practical method made it possible to measure the exact value of torque for clamping. Through this method it was also possible to calculate K - the empirical constant for the threads.

Glue line pressure:

Chung 1964 indicates that the required pressure between glue lines should be 100 psi (70 kN/m²). Similarly BS EN 302-2 recommended that the pressure between glue lines should be 60±10KN/m².