title: Ultimate moment capacity of bolted joint for cold-formed aluminium back-to-back channel sections

authors: Hasan, Zahid

subjects: Bolted joints

abstract: Cold-formed aluminium (CFA) channel sections are gaining popularity in structural applications as a lightweight and corrosion-resistant alternative to carbon steel, especially in coastal and aggressive environments. However, their effective use depends critically on the performance of their connections. This research investigates the structural behaviour of bolted moment connections in back-to-back CFA channel sections. Key factors such as web buckling, shear lag, and bending shear interaction were identified as influencing the ultimate moment capacity of these joints. An extensive numerical study of 1008 validated finite element (FE) models was conducted using ABAQUS. Moreover, validation was carried out based on experimental tests available in the literature. The Direct Strength Method (DSM) showed noticeable deviations from FE results in several cases, highlighting the limitations of DSM when applied to CFA sections. A parametric analysis was performed to examine the influence of cross-sectional size, thickness, web holes, and aluminium alloy grade and temper. Based on these findings, a new predictive equation is proposed for the reduced moment capacity of CFA back-to-back channel sections. The equation was rigorously assessed for reliability and accuracy, and it provides a practical tool for engineers designing CFA portal frame connections. 
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text: Ultimate moment capacity of bolted joint for cold-formed aluminium back-to-back channel sections Cold-formed aluminium (CFA) channel sections are gaining popularity in structural applications as a lightweight and corrosion-resistant alternative to carbon steel, especially in coastal and aggressive environments. However, their effective use depends critically on the performance of their connections. This research investigates the structural behaviour of bolted moment connections in back-to-back CFA channel sections. Key factors such as web buckling, shear lag, and bending shear interaction were identified as influencing the ultimate moment capacity of these joints. An extensive numerical study of 1008 validated finite element (FE) models was conducted using ABAQUS. Moreover, validation was carried out based on experimental tests available in the literature. The Direct Strength Method (DSM) showed noticeable deviations from FE results in several cases, highlighting the limitations of DSM when applied to CFA sections. A parametric analysis was performed to examine the influence of cross-sectional size, thickness, web holes, and aluminium alloy grade and temper. Based on these findings, a new predictive equation is proposed for the reduced moment capacity of CFA back-to-back channel sections. The equation was rigorously assessed for reliability and accuracy, and it provides a practical tool for engineers designing CFA portal frame connections. 
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year: 2026

title: Studies of the formation and properties of urea-formaldehyde resin adhesives

authors: Zeng, Huiyang

abstract: Urea-formaldehyde (UF) resin is used primarily as an adhesive for manufacturing wood panels (medium density fiberboard, particleboard and plywood). These are important New Zealand export products. A better understanding of the formation of UF resin will allow maximisation of its adhesive properties (high bonding strength) and minimisation of formaldehyde emissions (an adverse environmental effect). These improvements will enhance the competitive advantage of New Zealand resin products.

The research reported here has been directed primarily towards monitoring the UF reaction by Nuclear Magnetic Resonance spectroscopy (NMR), preparing UF resins, determining the performance of the resins produced and characterising the resins by high performance liquid chromatography (HPLC), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) methods.

The development of a dynamic (RAPID) NMR acquisition method has contributed to the identification of optimum conditions for UF resin manufacture. A series of NMR "snap-shots" of the UF reaction system over the entire reaction period has been obtained. A wide range of reaction conditions, eg formaldehyde to urea molar ratio, formaldehyde concentration, initial addition pH, condensation pH, addition reaction time and reaction temperature, have been investigated. From the species present and the changes in their relative concentrations during the reaction, optimum reaction conditions have been determined as:

Formaldehyde concentration: 35-46%
F/U molar ratio: 1.8-2.0
Temperature: 88°C
Addition reaction time: 25-30 min
Initial addition pH: 8.0-9.0
Condensation pH: 4.5-5.0

The dynamic (RAPID) NMR studies were complemented by HPLC characterisation of samples taken during the different reaction stages. The main low molecular weight species present in the UF reaction system have been identified. In general the HPLC results were consistent with those obtained by the dynamic (RAPID) NMR method.

Low molecular weight species were identified by electrospray mass spectrometry.

Molecular weight, molecular weight distribution and resin aging were investigated by the GPC method. The number average molecular weights of typical final UF resins were in the range of 600-800 Dalton. The weight average molecular weights of the same resins were in the range of 7000-10 000 Dalton.
A series of laboratory resins were prepared to test the appropriateness of the optimum reaction conditions predicted from the NMR and HPLC studies. Resin performance in wood panels was determined by measuring internal bond, formaldehyde emission and cold water swell. The effects of F/U molar ratio, resin loading and board thickness on the panel properties have also been determined. The results showed improvement in the internal bond and formaldehyde emissions.

Comparison of the experimental resin prepared under the optimum reactions with a commercial unmodified UF resin indicated that a 12% increase in internal bond. Formaldehyde emissions were similar.

It is clear from the results of this study that current manufacturing conditions for the production of unmodified UF resins are close to optimum. Future improvements are likely to be based upon structural and/or non-structural additives.

text: Studies of the formation and properties of urea-formaldehyde resin adhesives Urea-formaldehyde (UF) resin is used primarily as an adhesive for manufacturing wood panels (medium density fiberboard, particleboard and plywood). These are important New Zealand export products. A better understanding of the formation of UF resin will allow maximisation of its adhesive properties (high bonding strength) and minimisation of formaldehyde emissions (an adverse environmental effect). These improvements will enhance the competitive advantage of New Zealand resin products.

The research reported here has been directed primarily towards monitoring the UF reaction by Nuclear Magnetic Resonance spectroscopy (NMR), preparing UF resins, determining the performance of the resins produced and characterising the resins by high performance liquid chromatography (HPLC), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) methods.

The development of a dynamic (RAPID) NMR acquisition method has contributed to the identification of optimum conditions for UF resin manufacture. A series of NMR "snap-shots" of the UF reaction system over the entire reaction period has been obtained. A wide range of reaction conditions, eg formaldehyde to urea molar ratio, formaldehyde concentration, initial addition pH, condensation pH, addition reaction time and reaction temperature, have been investigated. From the species present and the changes in their relative concentrations during the reaction, optimum reaction conditions have been determined as:

Formaldehyde concentration: 35-46%
F/U molar ratio: 1.8-2.0
Temperature: 88°C
Addition reaction time: 25-30 min
Initial addition pH: 8.0-9.0
Condensation pH: 4.5-5.0

The dynamic (RAPID) NMR studies were complemented by HPLC characterisation of samples taken during the different reaction stages. The main low molecular weight species present in the UF reaction system have been identified. In general the HPLC results were consistent with those obtained by the dynamic (RAPID) NMR method.

Low molecular weight species were identified by electrospray mass spectrometry.

Molecular weight, molecular weight distribution and resin aging were investigated by the GPC method. The number average molecular weights of typical final UF resins were in the range of 600-800 Dalton. The weight average molecular weights of the same resins were in the range of 7000-10 000 Dalton.
A series of laboratory resins were prepared to test the appropriateness of the optimum reaction conditions predicted from the NMR and HPLC studies. Resin performance in wood panels was determined by measuring internal bond, formaldehyde emission and cold water swell. The effects of F/U molar ratio, resin loading and board thickness on the panel properties have also been determined. The results showed improvement in the internal bond and formaldehyde emissions.

Comparison of the experimental resin prepared under the optimum reactions with a commercial unmodified UF resin indicated that a 12% increase in internal bond. Formaldehyde emissions were similar.

It is clear from the results of this study that current manufacturing conditions for the production of unmodified UF resins are close to optimum. Future improvements are likely to be based upon structural and/or non-structural additives.

year: 2001

title: Ue Waerea

authors: Tuaupiki, Jackie Whetumarama

subjects: Waerea

abstract: Mai i Mōkau ki Tāmaki, Mangatoatoa, Pare-Waikato, Pare-Hauraki, Te Kaokaoroa o Pātetere, ko te whakapono, nā Tāwhaki i piki te poutama ki te tāhuhu matapu, ka riro mai i a ia ngā kete o te wānanga. E kīngia ai, ko te pūtake tērā o te mātauranga Māori. Hei tā Wiri (2001), nā te mātauranga Māori, ko te mātauranga Māori ā-waha. Nāna, ko te waiata. Nā te waiata, ko te karakia. Kei raro i te karakia, ko te takere kaupapa tēnei, ko te waerea. Ko te whāinga o tēnei tuhituhinga, he rangahau i ngā pūtake o te waerea me te āta titiro ki ngā kaupapa kei a ia me tōna kawe i roto i aua kaupapa i ngā wā o mua, ā, nō nāianei hoki. Ko te waerea te pane o ngā karakia Māori ki roto o Tainui, otirā, ki roto i ngētehi o ngā whakaritenga, ā, ka tirohia ngēnei whakaritenga e rere ai te waerea, pēnei i te tomo whare, i te tomo urupā, i te takahi whare, i te whakamānu waka me te maha o ngā mahi a te ao Māori ki roto o Tainui.

text: Ue Waerea Mai i Mōkau ki Tāmaki, Mangatoatoa, Pare-Waikato, Pare-Hauraki, Te Kaokaoroa o Pātetere, ko te whakapono, nā Tāwhaki i piki te poutama ki te tāhuhu matapu, ka riro mai i a ia ngā kete o te wānanga. E kīngia ai, ko te pūtake tērā o te mātauranga Māori. Hei tā Wiri (2001), nā te mātauranga Māori, ko te mātauranga Māori ā-waha. Nāna, ko te waiata. Nā te waiata, ko te karakia. Kei raro i te karakia, ko te takere kaupapa tēnei, ko te waerea. Ko te whāinga o tēnei tuhituhinga, he rangahau i ngā pūtake o te waerea me te āta titiro ki ngā kaupapa kei a ia me tōna kawe i roto i aua kaupapa i ngā wā o mua, ā, nō nāianei hoki. Ko te waerea te pane o ngā karakia Māori ki roto o Tainui, otirā, ki roto i ngētehi o ngā whakaritenga, ā, ka tirohia ngēnei whakaritenga e rere ai te waerea, pēnei i te tomo whare, i te tomo urupā, i te takahi whare, i te whakamānu waka me te maha o ngā mahi a te ao Māori ki roto o Tainui.

year: 2011-04