- 學位論文
EOTA與ACI混凝土用機械式緊固件評估準則之比較－以新型植筋錨栓為例
EOTA and ACI Assessment Documentations Comparison Study for Concrete Use Mechanical Fasteners－Rebar Screw Anchor Reference Characteristic Evaluation
若您是本文的作者，可授權文章由華藝線上圖書館中協助推廣。
摘要
混凝土用緊固件(錨栓)常應用於結構物聯結與補強工程，這類工程其通常具備30年至50年或較長之使用年限，為確保其於使用期間之安全性，除需仰賴良好設計與施工外，緊固件本身於生命週期間品質保證亦為確保其安全性不可缺少之要項，因此近年來歐洲與美洲地區工程組織均已建置完整錨栓特性評估制度，以確保其工程品質。我國新型螺紋植筋錨栓發明之目的為應用於混凝土結構補強用途，因此為推廣應用此新型錨栓有必要先執行與現今已廣泛應用於結構補強之化學植筋特性比較分析，與執行其基本工程特性評估。 本研究分別採用歐盟EOTA EAD及美國ACI 355評估準則，針對我國新型專利螺紋植筋錨栓執行與化學植筋錨栓黏結強度比較分析與該錨栓EOTA及ACI性能評估。本研究現階段範圍僅執行錨栓參考性評估試驗，研究試驗螺紋植筋錨栓為以磨擦焊接技術將碳鋼螺紋錨栓與鋼筋熔接為一體之施工元件，錨栓標稱直徑與植入深度分別為12 mm與150 mm，其螺紋段長度為109 mm，鋼筋段為#4鋼筋(直徑為12.7 mm)；化學植筋鋼筋段採用抗張強度為420 MPa之#4鋼筋，化學植筋黏結材採用國產環氧樹酯植筋膠，混凝土試驗構件標稱抗壓強度包括C20/25 (20.6 MPa)低強度及C50/60 (54.9 MPa)高強度混凝土。試驗範圍亦包括非開裂與開裂混凝土兩種條件，黏結性能評估以侷限抗張試驗為主，評估採用EOTA EAD 330499評估準則，試驗編號為R1及R2，植筋錨栓性能評估試驗以非侷限抗張試驗為主，於EOTA EAD 330232評估準則試驗編號為A1~A4；最後並執行EOTA EAD330232 F12最小邊距評估項目，除執行試驗比較分析外，本研究中並建置試驗所需開裂與非開裂混凝土設備與反力系統及試驗構件。 試驗結果顯示，植筋錨栓熔接處抗張強度大於鋼筋材料之抗張強度，應用於結構補強時應不致為補強材之最弱點。執行化學植筋錨栓與螺紋植筋錨栓侷限抗張黏結特性試驗比較分析結果顯示，侷限抗張試驗中螺紋植筋錨栓於C20/25及C50/60非開裂混凝土抗張強度分別為74.746 kN與84.818 kN；化學植筋錨栓於C20/25非開裂混凝土，有效埋入深度88.9 mm (7倍直徑)及108.5 mm抗張強度分別為83.836 kN與86.837 kN；然於C50/60非開裂混凝土，有效埋入深度88.9 mm 抗張強度為83.403 kN。植筋錨栓執行非侷限抗張試驗於C20/25非開裂混凝土及開裂混凝土平均強度分別為86.236 kN與60.723 kN，大部分試件呈現混凝土破壞加拉出破壞模式為主；於C50/60非開裂混凝土及開裂混凝土平均強度分別為88.391 kN與77.847 kN，前者破壞模式為鋼筋拉斷，後者因有裂紋的產生，試件呈現混凝土破壞加拉出破壞模式為主。螺紋植筋錨栓之侷限抗張試驗錨固強度雖然略低於化學錨栓，然在發生拉出破壞之試件，螺牙將孔壁之混凝土刮出，而螺牙本身皆無破損情形，可推斷此螺紋植筋錨栓之螺牙設計與鋼材強度有足夠的承載力。現階段研究顯示此植筋錨栓最小安裝邊距為125 mm。 由錨栓性能評估分析可知，EOTA與ACI規範均係經由90 %信度評估強度計算得初期特性強度，再依試驗混凝土抗壓強度經正規化分析程序以推算錨栓特性強度，並依有效面積推算特性黏結強度。由C20/25非開裂混凝土侷限抗張試驗，採EOTA及ACI準則評估化學錨栓與螺紋植筋錨栓於有效埋入深度為88.9 mm條件下，其特性黏結強度分別為21.176 N/mm2與21.574 N/mm2及11.257 N/mm2與11.745 N/mm2，採此兩種規範計算之特性黏結強度值對此兩種錨栓雖差異不大，且均大於規範需求強度10 N/mm2，但化學植筋黏結強度遠大於植筋錨栓，顯示此新型錨栓螺牙與混凝土雖咬合強度符合規範需求，但螺牙設計相對化學錨栓性能仍有改進空間。採EOTA及ACI評估準則評估螺紋植筋錨栓於C20/25混凝土執行非侷限抗張試驗，所得非開裂與開裂混凝土特性抗張強度分別為51.520 kN與64.401 kN及31.312 kN與44.722 kN；C50/60混凝土試驗組對應EOTA及ACI評估準則於開裂與非開裂混凝土特性抗張強度分別為64.442 kN與80.567 kN及41.565 kN與59.167 kN；分析結果顯示，如預期特性強度會隨混凝土抗壓強度增加而增加；EOTA評估準則分析數據較ACI準則所得數據為保守；當混凝土產生裂紋，錨栓之抗張能力將下降為非開裂情況的60～70 %，此下降情形採EOTA規範評估數值會折減約40 %，而採ACI規範評估數值會折減約30 %。 並根據ACI規範計算此螺紋植筋錨栓有效力k值，於C20/25低強度混凝土非開裂與開裂條件下，分析之k值分別為10.40與7.29，均介於規範非開裂與開裂混凝土條件下規範數值範圍內，表示此新型錨栓應用於低強度混凝土(17～28 MPa)結構物工程時符合規範需求；然由C50/60試驗組結果顯示均發生鋼筋拉斷破壞模式，其於非開裂與開裂混凝土條件下分析之k值分別為8.05與5.87，未符合C50/60高強度混凝土規範需求k值範圍內，顯示此螺紋植筋錨栓如需應用於高強度混凝土(50～60 MPa)結構物工程時，需改進其螺牙設計及製作時需採用高強度鋼筋製作。
並列摘要
Concrete fasteners are commonly used for structural connection and retrofitting engineering projects. These projects is normally having 30 to 50 year or even longer life span. To ensure the safety of these project during their service life, it not only requires good design and construction, but also needs a prove qualification of those anchor products during their life span. Therefore, European and American engineering societies had established anchor assessment system to ensure the safety of those anchor projects. The objective to the development of the new patent rebar screw anchor is for concrete structure retrofitting. Therefore, it is necessary to compare the bonding strength between the rebar screw anchor and chemical anchor, and to assessment the engineering properties of the new product. The objectives of this research include to compare the bonding strength between the new rebar screw anchor and typical chemical grout anchor and to conduct the quality assessment the new rebar screw anchor using EOTA and ACI anchor qualification guidelines. The scope of current research is limited to conduct the reference tests assessment only. The study rebar screw anchor is made by welding of a piece of screw anchor and a piece of rebar together. The screw anchor diameter and embedment depth are 12 mm and 150 mm. The screw section is 109 mm long. #4 rebar with diameter of 12.7 mm and yielding strength of 420 MPa is used to make the screw and to conduct the chemical grout anchor study. Local made epoxy chemical grout was used in the study. C20/25 (20.6 MPa) low strength and C50/60 (54.9 MPa) high strength concrete blocks with un-cracked and cracked condition were used in the evaluation tests. Anchor bonding strength evaluation was conducted using confined tension tests according to EOTA EAD 330499 R1 and R2 reference test programs. Rebar screw anchor assessment was conducted using unconfined tension tests based upon EOTA EAD 330232 A1~A4 reference test programs. In addition, EOTA EAD 330232 F12 test was used to evaluate the minimum edge distance for the rebar screw anchor. The cracked concrete member induced system with reaction frame was designed and built in the study. The test results indicated that the rebar screw anchor welding point strength was greater than the ultimate strength of the rebar, the welding point won’t be the weakest location for the rebar screw anchor. The bonding strengths of the rebar screw anchor in C20/25 and C50/60 un-cracked concrete were 74.746 kN and 84.818 kN; the bonding strength for the chemical anchor with 88.9 mm (7 d) and 108.5 mm embedment in C20/25 un-cracked concrete were 83.836 kN and 86.837 kN. Additional, the bonding strength in C50/60 un-cracked concrete with 88.9 mm embedment was 83.403 kN. The bonding strengths for rebar screw anchor in C20/25 un-cracked and cracked concrete were 86.236 kN and 60.723 kN. Concrete breakout and pullout failure was the primary failure mode observed for most test samples. The average tensile strengths for C50/60 un-cracked and cracked concrete were 88.391 kN and 77.847 kN. Rebar breakage was observed for the un-cracked samples. Anchor pullout was observed for cracked concrete samples. Even the confined tensile strength for the rebar screw anchor is less than that for the chemical anchor, the screw teeth were remain intact for most pullout failure cases. It indicated that strength of steel teeth is strong enough to resist the interlocking needs. The minimum edge distance was determined as 125 mm for the test rebar screw anchor in this study. According to the EOTA and ACI assessment guidelines the characteristic strength is determined based upon the 90 % confidence of normal distribution theory and normalized calculation based upon the ratio between the test concrete and nominal concrete strength. Furthermore, the characteristic bonding strength can be determined based upon the effective bonding area. According to the EOTA and ACI assessment guidelines of the chemical anchor and rebar screw anchor for C20/25 un-cracked concrete confined tension tests, the bonding strengths were 21.176 N/mm2, 21.574 N/mm2 and 11.257 N/mm2, 11.745 N/mm2, respectively. The analyzed bonding strengths according to these two guidelines were quite similar, there were all greater than the minimum bonding strength requirement, 10 N/mm2, for both specifications, however, the bonding strengths for chemical anchor were much greater than those for rebar screw anchor. It implied that the screw teeth design of the rebar screw anchor need some improvement in order to increase its bonding strength. According to the EOTA and ACI assessment guidelines of the rebar screw anchor for C20/25 un-cracked and cracked concrete using un-confined tension tests, the bonding strengths were 51.520 kN, 64.401 kN, and 31.312 kN, 44.722 kN, respectively. EOTA and ACI assessment guidelines of the rebar screw anchor for C50/60 un-cracked and cracked concrete using un-confined tension tests, the bonding strengths were 64.442 kN, 80.567 kN, and 41.565 kN, 59.167 kN, respectively. The analyses results indicated that the characteristic strength increased as increasing the concrete strength as expected. The values determined according to EOTA guideline was more conservative in comparing with those calculated by ACI guideline. The characteristic strength was decreased to about 60~70 % of un-cracked concrete value as cracked presented along anchor installation location within the test concrete block. The reduction rate was about 40 % for the analysis conducted using EOTA guideline, and the reduction rate was about 30 % for ACI guideline. The effectiveness k value was calculated for the rebar screw anchor installed in C20/25 un-cracked and cracked low strength concrete, the k values were 10.40 and 7.29, respectively, which are all within the guideline specified ranges. It implied that the rebar screw concrete is suitable for retrofitting application for low strength (17~28 MPa) concrete. However, the most assessment tests for the rebar screw anchor installed in C50/60 high strength concrete, rebar yielding failure or rebar-screw anchor welding point breakage failure was observed. The effective k values for un-cracked and cracked concrete were 8.05 and 5.87, respectively. There are all unsatisfied the guideline specification ranges. It implied that the rebar screw concrete is un-suitable for retrofitting application for high strength (50~60 MPa) concrete. The teeth of the rebar screw anchor either needs some modification or high strength rebar shall be used for the high strength concrete retrofitting application.
參考文獻
1. ACI 318-19, 2019, Building Code Requirements for Structural Concrete and Commentary, American Concrete Institute, ACI Committee 318, Detroit, Michigan.
2. ACI 355.2-19, 2019, Qualification of Post-Installed Mechanical Anchors in Concrete and Commentary, American Concrete Institute, ACI Committee 355, Detroit, Michigan.
3. ACI 355.4-19, 2019, Qualification of Post-Installed Adhesive Anchors in Concrete and Commentary, American Concrete Institute, ACI Committee 355, Detroit, Michigan.
4. ASTM E488, 2018, Standard Test Methods for Strength of Anchors in Concrete Elements, American Standard of Tests and Material.
5. EN 1992-4, 2017, Eurocode 2: Design of concrete structures － Part 4: Design of fastenings for use in concrete, European Organization for Technical Assessment.