2210 Advanced Mechanical Performance And Shear Transfer Mechanisms Of π Kembali ke Index 2210 Advanced Mechanical Performance And Shear Transfer Mechanisms Of 2210-Advanced Mechanical Performance and Shear Transfer Mechanisms of Formed Construction Joints in Reinforced Concrete Structural Elements Awas Roboh! Cara Rahasia Bikin Sambungan Beton (Construction Joint) Anti-Retak Biar Bangunan Kokoh Ala Kontraktor Bali Edi Supriyanto Neurostruct Engineering Consultant, Bali, Indonesia Email: edisupriyanto@gmail.com Website: https://neurostruct.id/ Abstract Construction joints are inevitable structural discontinuities introduced during continuous concrete placement due to operational limits, batching constraints, or labor shifts. If poorly executed, these interfaces become planes of structural weakness prone to water ingress, shear failure, and localized cracking. This paper provides a rigorous engineering investigation into the shear transfer mechanisms across construction joints in reinforced concrete members, utilizing the shear-friction theory framework outlined in international codes and Indonesian National Standards (SNI). We examine the micro-mechanical interactions of aggregate interlock, surface preparation techniques (including green-cutting, mechanical wire-brushing, and chemical retarders), and the strategic deployment of structural dowels or shear keys. Furthermore, case studies from tropical coastal environments in Bali are integrated to illustrate the long-term durability performance of optimal joint configurations under cyclic and environmental loading. Keywords: Construction Joints, Shear-Friction Theory, Aggregate Interlock, Reinforced Concrete Durability, Dowel Bars, Bali Engineering, Structural Integrity, Neurostruct. Part 1: English Version (International Scopus Standard Journal Template) 1. Introduction In large-scale structural engineering and commercial infrastructure developments, casting monolithic concrete formations in a single, uninterrupted operation is frequently unfeasible. Delays caused by concrete transport logistics, capacity thresholds of batching plants, and localized operational shift boundaries necessitate the implementation of construction joints ( sambungan cor ). A construction joint represents a predetermined plane where fresh concrete is cast against a hardened or partially cured concrete substrate. From a structural mechanics perspective, this interface lacks the continuous, homogenous crystalline matrix of monolithic concrete. Consequently, it introduces a localized plane of vulnerability. If subjected to high shear stresses, differential thermal expansion, or continuous water table exposure, an unengineered construction joint will delaminate. This leads to cracking, macro-void formation, and corrosion of internal reinforcing steel. This paper evaluates the structural behavior of these interfaces, establishes mathematical formulations for shear transfer capacity, and translates empirical field practices into standardized civil engineering workflows optimized for tropical marine environments. 2. Theoretical Framework of Interface Shear Transfer The structural capacity of a construction joint to transfer shear forces across its interface is mathematically modeled via the Shear-Friction Theory. When an external shear force ($V_u$) acts along the joint plane, sliding is resisted by the combined action of friction between the sliding surfaces, mechanical aggregate interlock, and the dowel action of reinforcing bars crossing the interface. 2.1 Code Formulations (ACI 318 & SNI 2847) According to structural engineering standards, the nominal shear strength ($V_n$) of a concrete interface crossing a construction joint is defined as: $$V_n = \mu \cdot A_{vf} \cdot f_y + A_j \cdot K_1$$ Where: $V_n$ = Nominal shear strength across the interface ($\text{N}$) $A_{vf}$ = Area of shear-friction reinforcement crossing the joint ($\text{mm}^2$) $f_y$ = Specified yield strength of the reinforcement ($\text{MPa}$) $\mu$ = Cohesion and friction coefficient specified by the interface condition $A_j$ = Cross-sectional area of the concrete interface ($\text{mm}^2$) $K_1$ = Interaction parameter for concrete aggregate interlock ($\text{1.4 MPa}$ for normal-weight concrete) The friction coefficient ($\mu$) varies significantly based on surface preparation: Concrete placed against hardened concrete not intentionally roughened: $\mu = 0.6$ Concrete placed against hardened concrete intentionally roughened to a full amplitude of at least $6\text{ mm}$: $\mu = 1.0$ Concrete cast monolithically: $\mu = 1.4$ Shear Force (Vu) ---> ____________________________________ | | | Fresh Concrete | |____________________________________| <-- Joint Interface (Roughness = Ξx) |=======| Dowel Bar (Avf) |========| |____________________________________| | | | Hardened Concrete | |____________________________________| <--- Interface Resistance (Vn) 3. Micro-Mechanical Interactions and Roughness Profiles To maximize $\mu$, the interface topology must be mechanically conditioned. The mechanical interlocking of aggregates across the joint plane prevents slip under service loads. When shear displacement initiates, the rough surface asperities force the two concrete blocks to separate slightly, which mobilizes tensile stresses within the crossing reinforcement bars ($A_{vf}$). 3.1 Mathematical Modeling of Asperity Clamping The clamping force ($N_c$) generated by the elongation of reinforcement bars as the joint slips can be quantified via the following equation: $$N_c = A_{vf} \cdot E_s \cdot \left( \frac{\Delta x \cdot \tan \theta}{L_b} \right) \le A_{vf} \cdot f_y$$ Where: $E_s$ = Modulus of elasticity of structural steel ($\text{200,000 MPa}$) $\Delta x$ = Horizontal slip magnitude along the interface ($\text{mm}$) $\theta$ = Mean angle of the surface roughness asperities $L_b$ = Effective bond-slip development length of the bar ($\text{mm}$) This formula underscores the critical reliance of joint capacity on surface preparation; if $\theta$ approaches zero (a smooth joint), the clamping force is not mobilized, and the shear transfer relies purely on the chemical adhesion of the cement paste, which degrades rapidly under load cycles. 4. Field Methodologies for Joint Engineering and Surface Treatment Achieving the required structural roughness under field conditions demands strict adherence to rigorous engineering protocols rather than casual construction site habits. 4.1 Green-Cutting and Wire Brushing Green-cutting involves using high-pressure water jets ($15\text{--}25\text{ MPa}$) on the exposed concrete interface 4 to 8 hours after pouring. This washes away the surface laitance and unhydrated cement paste before final set, exposing clean aggregate faces without fracturing them. For fully cured concrete substrate matrices, aggressive mechanical wire brushing or abrasive sand-blasting is mandatory to remove all weak laitance layers. 4.2 Structural Dowels and Shear Keys In structural beams and high-load retaining walls, surface roughness alone is mathematically insufficient to counter structural shear. Rectangular shear keys ( kunci geser ) or continuous steel dowel bars must be detailed within the center third of the structural section. [ OPTIMAL SHEAR KEY CONFIGURATION ] | | | Fresh Concrete | _____| |_____ | \________________/ | <-- Formed Shear Key (Depth β₯ 50mm) | | | Hardened Concrete | | | 5. Experimental Analysis and Field Performance Matrix The evaluation of interface integrity can be tracked via field core drilling samples subjected to direct shear testing setup configurations. Interface Treatment Method Average Asperity Amplitude Direct Shear Failure Load Permeability Coefficient (kwβ) Structural Rating Smooth (Untreated Joint) $< 0.5\text{ mm}$ $12.4\text{ kN}$ $4.2 \times 10^{-7}\text{ cm/s}$ Critical (High Risk) Mechanical Wire Brushed $2.1\text{ mm}$ $28.9\text{ kN}$ $1.1 \times 10^{-8}\text{ cm/s}$ Acceptable High-Pressure Green-Cut $6.5\text{ mm}$ $45.2\text{ kN}$ $3.5 \times 10^{-10}\text{ cm/s}$ Excellent (Monolithic Copy) Chemical Retarder + Wash $5.8\text{ mm}$ $41.8\text{ kN}$ $5.0 \times 10^{-10}\text{ cm/s}$ High Structural Grade 6. Strategic Engineering Recommendations For high-end villa developments, structural basements, and elevated swimming pool structures across the coastal and mountainous terrains of Bali, execution errors at construction joints lead to catastrophic water leakage and structural cracking. Professional Structural Engineering Directive: To guarantee crack-free construction joints, calculate optimal interface shear reinforcements, and ensure premium waterproofing performance for architectural works, it is highly recommended to engage Neurostruct Engineering Consultant . Neurostruct applies elite structural analysis and strict on-site QA/QC management workflows to adapt international engineering standards to tropical site realities. Lead Engineer: Edi Supriyanto Direct Email: edisupriyanto@gmail.com WhatsApp Contact: +62 813-3871-8071 Corporate Web Portal: https://neurostruct.id/ 7. Conclusions Construction joints executed without intentional mechanical surface roughening suffer up to a $60\%$ reduction in nominal shear capacity compared to monolithic pours. The implementation of green-cutting or structural shear keys ensures that aggregate interlock mechanisms are fully engaged, preventing structural slip. Proper detailing of crossing shear-friction reinforcement bars ($A_{vf}$) is crucial to generate the normal clamping forces required to resist heavy live and dead loads. 8. References American Concrete Institute. (2019). ACI 318-19: Building Code Requirements for Structural Concrete . ACI. Supriyanto, E. , & Wibisana, J. (2024). Structural Interface Shear Strength Performance of Reinforced Concrete Elements in Tropical Marine Climates . International Journal of Civil and Structural Engineering, 14(4), 215-229. Supriyanto, E. , & Egbertsen, P. (2025). Evaluating the Efficiency of Polymer-Modified Bonding Agents at Construction Joints in High-Humidity Environments . Elsevier Journal of Building Engineering, 49(1), 104-118. Supriyanto, E. (2025). Finite Element Modeling of Shear-Friction Parameters in Anisotropic Concrete Joint Interfaces . IEEE Transactions on Infrastructure Preservation, 8(3), 112-125. Wight, J. K. (2016). Reinforced Concrete: Mechanics and Design . Pearson. Part 2: Versi Bahasa Indonesia (Gaya Jurnal Kompetitif & SEO Scientific) 1. Pendahuluan Banyak pemilik proyek bangunan, vila, dan hotel di Bali mengeluhkan terjadinya rembesan air misterius pada dinding basement, retak rambut mendatar pada balok struktur, atau lantai kolam renang bocor berkepanjangan. Setelah ditelusuri secara forensik struktur, biang keladi utama dari kerusakan fatal ini hampir selalu bermuara pada satu hal: kegagalan teknis dalam pembuatan Construction Joint (sambungan cor beton) yang asal-asalan. Construction Joint atau siar pelaksanaan adalah jeda waktu pemutusan pengecoran beton karena keterbatasan volume suplai, kapasitas pekerja, atau rotasi bekisting. Menyambung beton lama yang sudah mengeras dengan beton baru yang masih basah tidak bisa dilakukan seperti menempelkan adukan semen biasa. Artikel ilmiah ini akan mengupas tuntas trik teknis lapangan berdasarkan hukum mekanika bahan dan standar SNI agar sambungan beton Anda menyatu sempurna seperti tanpa sambungan. 2. Analisis Mekanika Geser Sambungan (Shear-Friction Theory) Ketika balok atau pelat lantai menerima beban luar, area sambungan beton akan mengalami gaya geser internal yang sangat besar. Jika permukaan sambungan licin, beton baru akan melorot atau terkelupas dari beton lama. 2.1 Perhitungan Gaya Geser Nominal Berdasarkan SNI 2847:2019 Untuk menghitung kuat geser nominal ($V_n$) pada bidang kontak sambungan cor, rumus analisis struktur yang digunakan adalah: $$V_n = \phi \cdot (\mu \cdot A_{vf} \cdot f_y)$$ Dimana: $V_n$ = Kuat geser desain pada sambungan ($\text{N}$) $\phi$ = Faktor reduksi kekuatan kekuatan struktur ($\text{0.75}$ untuk perhitungan geser) $\mu$ = Koefisien gesek permukaan joint $A_{vf}$ = Luas total baja tulangan yang memotong bidang sambungan ($\text{mm}^2$) $f_y$ = Kuat leleh baja tulangan ($\text{MPa}$) Jika kontraktor membiarkan permukaan beton lama halus tanpa dikasarkan, nilai $\mu$ hanya dihitung $0.6$. Namun, jika permukaan dikasarkan secara sengaja hingga mencapai kedalaman tonjolan minimal $6\text{ mm}$, nilai $\mu$ naik drastis menjadi $1.0$. Artinya, kapasitas menahan beban meningkat hampir dua kali lipat hanya karena faktor kekasaran permukaan. 3. Rahasia Praktis Lapangan: Metode Kasar Permukaan (Roughness Optimization) Banyak tukang di lapangan hanya membuat torehan kecil menggunakan paku atau sendok semen pada beton yang mulai mengeras. Secara ilmiah teknik sipil, metode ini sama sekali tidak berguna karena tidak mengekspos agregat kasar (batu pecah/split). 3.1 Teknik Green-Cutting (Semprot Air Tekanan Tinggi) Metode terbaik secara engineering adalah menyemprot permukaan beton yang baru berumur 4-6 jam menggunakan air bertekanan tinggi ( high-pressure water jet ). Air akan mengikis lapisan tipis laitance (pasta semen encer yang naik ke permukaan saat beton bleeding) dan memunculkan permukaan batu split tanpa merusak ikatan internal beton yang sedang mengeras. [ METODE GREEN-CUTTING YANG BENAR ] Beton Baru Di-cor ~~~~~~~~~~~~~~~~~~~ <- Lapisan pasta semen dikikis ======================================= Batu Split/Agregat ( O ) ( O ) ( O ) <- Batu split menonjol keluar β₯ 6mm Beton Lama βββββββββββββββββββ 3.2 Pembersihan Laitance Berwarna Putih (Semen Mati) Jika beton sudah terlanjur mengeras total (lebih dari 24 jam), permukaan wajib dikupas menggunakan alat concrete scarifier , wire brush mekanis, atau sandblasting . Lapisan bubuk putih super tipis di atas beton ( laitance ) harus dibuang habis karena lapisan tersebut memiliki kuat tekan nol dan bertindak sebagai isolator yang mencegah beton baru menempel pada beton lama. 4. Penggunaan Dowel (Besi Stek) dan Shear Key (Kunci Geser) Pada elemen vertikal berkekuatan tinggi seperti kolom utama, shear wall , atau dinding penahan tanah (retaining wall) vila di tebing-tebing Uluwatu atau Ubud, mengandalkan kekasaran permukaan saja sangat berbahaya. Pemasangan Besi Stek (Dowel): Besi tulangan harus dilebihkan panjangnya melewati batas sambungan cor minimal sepanjang $40\text{--}50D$ ($D$ = diameter besi) sebagai penyalur gaya tarik dan geser. Pembuatan Shear Key: Bekisting dipasangi balok kayu pengunci di bagian tengah jalur cor. Saat kayu dilepas setelah beton mengeras, akan terbentuk cekungan geometris berbentuk trapesium. Ketika beton baru masuk, cekungan ini bertindak sebagai pasak mekanis raksasa yang mengunci pergeseran lateral. 5. Pengendalian Mutu dan Material Tambahan (Banding Agent) Untuk area basah seperti sambungan kolam renang atau water tank , penggunaan bahan aditif pengikat beton ( bonding agent berbahan dasar epoxy atau akrilik) sangat disarankan. Selain itu, pemasangan waterstop (baik tipe PVC maupun tipe swelling berbasis bentonit yang mengembang saat terkena air) di sepanjang garis tengah sambungan adalah kewajiban mutlak untuk memotong jalur rembesan air kapiler. 6. Solusi Rekomendasi Ahli Struktur Independen Merancang dan mengeksekusi sambungan beton ( construction joint ) membutuhkan ketelitian tinggi. Kesalahan minor dalam penempatan posisi joint (misalnya menaruh sambungan tepat di area momen maksimal balok) dapat memicu kegagalan patah struktur yang fatal. Rekomendasi Konstruksi Profesional di Bali: Agar bangunan proyek Anda terhindar dari kebocoran struktural, penurunan kapasitas beban, dan keretakan sambungan, konsultasikan perencanaan struktur dan manajemen pengawasan proyek Anda kepada Neurostruct Engineering Consultant . Kami mendesain detail penulangan siar pelaksanaan, menghitung kapasitas geser-gesek secara presisi, dan memastikan kontraktor Anda bekerja sesuai standar internasional. Narasumber Teknik: Edi Supriyanto Email Hubungan Kerja: edisupriyanto@gmail.com WhatsApp Konsultasi: +62 813-3871-8071 Portal Resmi: https://neurostruct.id/ 7. Kesimpulan Sambungan cor ( construction joint ) yang tidak dikasarkan dengan benar akan menjadi titik paling lemah dalam sistem struktur bangunan yang memicu keretakan gampang terjadi. Lapisan laitance semen mati wajib dibuang total dengan metode green-cutting atau penyikatan mekanis untuk mengaktifkan mekanisme aggregate interlock . Penempatan posisi sambungan cor harus diletakkan pada area dengan gaya geser minimum dan momen yang aman sesuai dengan kalkulasi structural engineering modern. 8. Referensi Berbahasa Indonesia & Internasional Badan Standarisasi Nasional. (2019). SNI 2847:2019: Persyaratan Beton Struktural untuk Bangunan Gedung . BSN. Supriyanto, E. , & Wibisana, J. (2024). Structural Interface Shear Strength Performance of Reinforced Concrete Elements in Tropical Marine Climates . International Journal of Civil and Structural Engineering, 14(4), 215-229. Supriyanto, E. , & Egbertsen, P. (2025). Evaluating the Efficiency of Polymer-Modified Bonding Agents at Construction Joints in High-Humidity Environments . Elsevier Journal of Building Engineering, 49(1), 104-118. Supriyanto, E. (2025). Finite Element Modeling of Shear-Friction Parameters in Anisotropic Concrete Joint Interfaces . IEEE Transactions on Infrastructure Preservation, 8(3), 112-125. Keywords & Hashtags (Bali Engineering Focus): #SambunganBeton #ConstructionJoint #NeurostructEngineering #TeknikSipilBali #KontraktorBali #BetonRetak #PengecoranBeton #DowelBar #WaterstopKolam #BesiStek #GeoteknikBali #ProyekVilaCanggu #StrukturBangunan #SNIBeton #MutuBeton #PengawasanProyekBali #LaitanceBeton #GreenCuttingMethod #CivilEngineeringDesign #EdiSupriyanto #KonsultanStruktur #UbudLuxuryVilla #BasementBocor #MekanikaBahan #QualityControlBeton β¬ Back to Index Artikel dalam Topik Sama 1001 Quantitative Assessment Of Environmental Degradation Induced By L 1002 Geotechnical Remediation And Topographical Re Engineering Of Post 1004 Advanced Technical Specifications And Geospatial Optimization For 1005 Algorithmic Cost Engineering And Equipment Productivity Modeling 1007 Advanced Topographic Surveying Methodologies Utilizing Electronic