Government of India • Ministry of Road Transport & Highways
Structural Health Monitoring
of Highway Bridges
Technical Specification Document
Document No: TS-SHM-HB / 2026 / Rev-A
Classification: Advisory & Technical Specification
Scope: All National Highways, Expressways &
State Highway Bridges in India
Prepared By: Technical Advisory Division
Status: Final Draft
Version 1.0 — August 2026
Table of Contents
- Introduction & Purpose
- Scope & Applicability
- Definitions & Terminology
- Normative References & Governing Standards
- SHM System Classification & Selection Criteria
- Instrumentation & Sensor Requirements
- Data Acquisition, Transmission & Storage
- Data Processing, Analytics & Threshold Alerts
- Installation, Commissioning & Calibration
- Operation, Maintenance & Lifecycle Management
- Reporting, Compliance & Documentation
- Bid Evaluation & Vendor Qualification
- Annexures
1. Introduction & Purpose
1.1 Background
India possesses one of the largest road networks in the world, spanning over 6.3 million kilometres,
with more than 1,70,000 bridges on the National Highway network alone. As infrastructure ages and
traffic loads intensify — often exceeding original design assumptions — the structural integrity
of these bridges becomes a critical safety and economic concern. Traditional periodic visual
inspections, while essential, cannot provide real-time insight into structural behaviour under
live loading, during extreme weather events, or as deterioration progresses between inspections.
Structural Health Monitoring (SHM) bridges this gap by deploying permanent or semi-permanent sensor
networks that continuously measure key parameters — acceleration, strain, displacement, tilt,
temperature, and corrosion activity — enabling data-driven decision-making for maintenance,
load rating, and emergency response.
1.2 Purpose of This Document
This Technical Specification Document serves five primary objectives:
- Establish minimum technical requirements for SHM systems on highway bridges in India,
aligning with the Indian Roads Congress (IRC), Ministry of Road Transport & Highways (MORTH),
and National Highways Authority of India (NHAI) guidelines.
- Provide a standardised procurement framework for instrumentation, data acquisition,
analytics, and reporting platforms.
- Define acceptance criteria, performance thresholds, and alarm protocols
consistent with Indian climatic, seismic, and traffic conditions.
- Enable interoperability with the proposed National Bridge Inventory and
Asset Management System.
- Serve as a reference for Design-Build-Finance-Operate-Transfer (DBFOT) and
Engineering-Procurement-Construction (EPC) contract specifications.
1.3 Target Audience
- NHAI / MORTH project directors and regional officers
- State Public Works Departments (PWDs) and road development corporations
- Concessionaires and EPC contractors
- SHM system integrators and instrumentation vendors
- Academic and research institutions engaged in bridge engineering
- Independent engineers and proof-checking consultants
2. Scope & Applicability
2.1 Asset Categories Covered
| Bridge Type | Examples | SHM Mandate |
|---|
| Major Bridges |
Cable-stayed, suspension, extradosed, arch (span ≥ 150 m) |
Mandatory — Level-3 (full SHM suite) |
| Long-Span Bridges |
Continuous box-girder, segmental (span ≥ 100 m) |
Mandatory — Level-2 (comprehensive SHM) |
| Important Bridges |
Bridges on expressways, in seismic zone IV/V, scour-critical,
or with ADT > 75,000 |
Mandatory — Level-2 |
| Standard Bridges |
Simply-supported PSC/RCC, composite steel-concrete (span 30–100 m) |
Recommended — Level-1 (select parameters) |
| Minor Bridges & Culverts |
Span < 30 m, slab/box culverts |
Optional — based on condition rating |
| Heritage / Special Bridges |
Masonry arch, steel truss, movable bridges |
Case-by-case — as directed by NHAI/MORTH |
2.2 SHM Levels Defined
| Level | Description |
|---|
| Level-1 |
Essential monitoring: tilt/inclination at bearings, ambient vibration
(acceleration) at mid-span, temperature at deck and ambient.
Minimum one data logger. Local alarm only. |
| Level-2 |
Comprehensive monitoring: adds strain at critical sections,
displacement at expansion joints, scour at piers,
corrosion potential in reinforced concrete,
wind speed/direction. Cloud-connected dashboard with SMS/email alerts. |
| Level-3 |
Complete SHM suite: all Level-2 parameters plus stay-cable / hanger
force monitoring (via accelerometers or load cells),
GNSS-based deck displacement, weigh-in-motion (WIM) integration,
seismic strong-motion accelerographs,
weather station, CCTV for traffic.
Full digital twin integration. |
3. Definitions & Terminology
| Term | Definition |
|---|
| SHM | Structural Health Monitoring — the process of implementing a damage
detection and characterisation strategy for engineering structures using
permanently installed sensors. |
| DAQ | Data Acquisition System — the hardware that samples, digitises, and
transmits analogue sensor signals. |
| DT | Digital Twin — a virtual representation of the physical bridge that
receives real-time sensor data and can be used for simulation and
predictive analytics. |
| NBI | National Bridge Inventory — the centralised database of all bridges
on the National Highway network, as maintained by NHAI. |
| BMS | Bridge Management System — the software platform used to schedule
inspections, track condition ratings, and prioritise maintenance. |
| Modal Parameters | Natural frequencies, mode shapes, and damping ratios extracted from
vibration data. |
| FE Model | Finite Element Model — a numerical model of the bridge used for
structural analysis and model updating. |
| OMA | Operational Modal Analysis — extraction of modal parameters using
ambient (traffic/wind) excitation only. |
| WIM | Weigh-in-Motion — system that measures axle loads of vehicles
travelling at highway speeds without stopping. |
| CBR | Condition-Based Rating — bridge condition index derived from SHM
data, complementing visual inspection ratings. |
| MTBF | Mean Time Between Failures — reliability metric for SHM components. |
| PoE | Power over Ethernet — delivers DC power and data over a single
twisted-pair cable per IEEE 802.3. |
4. Normative References & Governing Standards
4.1 Indian Standards (IRC / MORTH / BIS)
| Standard | Title | Relevance |
|---|
| IRC:SP:35-2015 |
Guidelines for Inspection and Maintenance of Bridges |
Establishes condition rating methodology; SHM data must integrate with
inspection cycles defined herein. |
| IRC:SP:54-2014 |
Project Preparation Manual for Bridges |
Mandates SHM in the planning phase for major and special bridges. |
| IRC:SP:77-2008 |
Guidelines for Design of Highway Bridges |
Design parameters and load assumptions used as baseline for SHM
threshold setting. |
| IRC:112-2019 |
Code of Practice for Concrete Road Bridges |
Material properties, durability requirements, and crack-width
limits used for SHM alarm thresholds. |
| IRC:6-2017 |
Loads & Load Combinations |
Class 70R, Class A, and special vehicle loads; overload detection
thresholds derived from these. |
| IRC:22-2015 |
Composite Construction (Section VI) |
Relevant for composite steel-concrete bridge monitoring. |
| IRC:78-2014 |
Foundations & Substructure |
Scour monitoring and foundation tilt thresholds. |
| MORTH Spec. (5th Rev, 2013) |
Specifications for Road & Bridge Works |
Section 1000–2900: Material, workmanship, and testing requirements
applicable to sensor installation. |
| IS 456:2000 |
Plain & Reinforced Concrete — Code of Practice |
Deflection limits; durability provisions. |
| IS 800:2007 |
Steel Structures — Code of Practice |
Steel stress limits and fatigue provisions. |
| IS 1893 (Part 1):2016 |
Earthquake-Resistant Design |
Seismic zone factors; strong-motion trigger thresholds. |
| IRC:SP:114-2018 |
Guidelines for Seismic Design of Road Bridges |
Performance objectives for post-earthquake SHM assessment. |
| NHAI Circular 11.3/2018 |
Bridge Health Monitoring System on Major Bridges |
Directive mandating SHM on all major bridges on National Highways. |
4.2 International Standards
| Standard | Title |
|---|
| ISO 14963:2003 | Mechanical vibration and shock — Guidelines for dynamic tests and
investigations on bridges and viaducts |
| ISO 4866:2010 | Mechanical vibration and shock — Vibration of fixed structures —
Guidelines for the measurement of vibrations and evaluation of their
effects on structures |
| ISO 16587:2004 | Mechanical vibration and shock — Performance parameters for
Structural Health Monitoring of structures |
| SAMCO F08b (2006) | Guidelines for Structural Health Monitoring — F08a (Glossary),
F08b (Design), F08c (Implementation) |
| FHWA-HIF-19-035 | Guidelines for Bridge Management Systems (AASHTO) |
| BS ISO 18649:2004 | Mechanical vibration — Evaluation of measurement results from dynamic
tests on structures |
| EN 1990:2002 (Eurocode 0) | Basis of structural design — reliability differentiation |
| IEC 60751 | Industrial platinum resistance thermometers |
| IEEE 1451 | Smart transducer interface standards |
5. SHM System Classification & Selection Criteria
5.1 Risk-Based Classification Matrix
The required SHM level shall be determined by a weighted risk score (R):
R = S × C × V × D × Re
| Factor | Weight | 1 | 2 | 3 | 4 | 5 |
|---|
| S — Span (m) | 1.0 | < 30 | 30–60 | 60–100 | 100–150 | ≥ 150 |
| C — Consequence of Failure | 1.5 | Local road | SH/MDR | NH (low traffic) | Expressway / NH | Strategic / Defence |
| V — Vulnerability | 1.2 | New (<5 yr) | Good condition | Fair | Poor / ageing | Critical / distressed |
| D — Design Complexity | 1.0 | Simple span | Continuous | Balanced cantilever | Arch / extradosed | Cable-stayed / suspension |
| Re — Redundancy | 1.3 | Highly redundant | Multiple girders | Twin box | Single box | Fracture-critical |
Threshold: R ≥ 55 → Level-3 (Mandatory) | 25 ≤ R < 55 → Level-2 | R < 25 → Level-1
5.2 Bridge-Specific Sensor Deployment Guide
| Bridge Type | Critical Monitoring Locations | Key Parameters |
|---|
| Cable-Stayed |
Pylon top/base, stay cables (every 4th cable), deck at L/4, L/2, 3L/4 |
Cable force, pylon tilt, deck displacement, acceleration, wind, temperature |
| Suspension |
Tower top/base, main cables (anchorages), hangers, deck mid-span |
Cable tension, tower tilt, hanger force, deck modal, wind, GNSS |
| Extradosed |
Pylon, extradosed cables, deck at L/2 |
Cable force, pylon inclination, deck strain, acceleration |
| Steel Arch |
Crown & springing of arch rib, hangers, deck beam |
Arch rib strain, acceleration, hanger tension, temperature |
| Balanced Cantilever (PSC) |
Pier top segment, L/4 segments, mid-span closure, bearing |
Concrete strain, deflection, bearing displacement, temperature gradient |
| Segmental Box Girder |
Mid-span soffit, web (shear-critical), pier diaphragm, bearing |
Strain, deflection, acceleration, bearing movement |
| Composite Steel-Concrete |
Steel girder bottom flange, shear connectors zone, mid-span |
Strain, acceleration, bearing displacement, fatigue cycle count |
| Simply-Supported PSC/RCC |
Mid-span soffit, bearing, pier top |
Deflection, bearing tilt, acceleration, scour |
6. Instrumentation & Sensor Requirements
6.1 General Sensor Specifications
All sensors shall comply with the following:
- Environmental: Operating temperature −10 °C to +70 °C (Indian desert to Himalayan conditions);
IP67 minimum enclosure (IP68 if submersible or exposed to monsoon flooding).
- Humidity: 0–100% RH, condensing.
- Electromagnetic Compatibility: IEC 61000-4 series — immunity to lightning-induced surges
(common in Indian monsoon) per IEC 62305.
- Vibration / Shock: Withstand transport on Indian roads as per IS 9000.
- Calibration: Factory-calibrated with traceable certificate to NABL-accredited lab;
field recalibration interval not exceeding 24 months.
- Connectors: Military-grade (MIL-DTL-38999 or equivalent) with gold-plated contacts;
all outdoor junctions in IP68 junction boxes with desiccant breathers.
- Service Life: Minimum 15 years for embedded sensors; 10 years for surface-mounted.
6.2 Sensor Type Specifications
6.2.1 Accelerometers
| Parameter | Level-1 / 2 | Level-3 |
|---|
| Type | MEMS capacitive or force-balance servo | Force-balance servo (preferred) |
| Range | ±2 g | ±4 g (seismic) |
| Frequency Response | DC to 200 Hz (−3 dB) | DC to 400 Hz (−3 dB) |
| Noise Floor | ≤ 3 µg/√Hz | ≤ 1 µg/√Hz |
| Resolution | ≤ 1 µg | ≤ 0.1 µg |
| Dynamic Range | ≥ 120 dB | ≥ 140 dB |
| Sensitivity | 2.5 V/g or 10 V/g (selectable) | 10 V/g |
| Output | ±10 V differential or IEPE | ±10 V differential |
| Mounting | Stud / adhesive / levelling base plate | Stud with levelling base plate |
6.2.2 Strain Gauges
| Parameter | Electrical Resistance | Vibrating Wire (VW) | Fibre Bragg Grating (FBG) |
|---|
| Gauge Length | 5–120 mm | 150–300 mm | 10–100 mm |
| Range | ±3000 µε | ±3000 µε | ±5000 µε |
| Resolution | 0.5 µε | 0.5 µε | 0.1 µε |
| Long-term Stability | Fair | Excellent | Excellent |
| EMI Immunity | Poor — requires shielding | Good | Excellent |
| Dynamic Capability | ≤ 1 kHz | ≤ 50 Hz | ≤ 5 kHz |
| Recommended Use | Short-term tests | Long-term concrete strain | Long-term; multi-parameter; explosive zones |
| Embedded Variant | Available | Available (concrete embedment) | Available |
Preference: For permanent long-term monitoring on concrete bridges, Vibrating Wire (VW) gauges
are recommended for their zero-drift stability over decades. FBG sensors are recommended for steel bridges
and in environments with high electromagnetic interference (e.g., near railway traction power,
overhead HV lines common near Indian highways).
6.2.3 Displacement / Crack Sensors
| Parameter | Specification |
|---|
| Type | LVDT, draw-wire potentiometer, or magnetostrictive |
| Range | 0–50 mm (crack), 0–500 mm (expansion joint) |
| Resolution | ≤ 0.01 mm |
| Accuracy | ±0.5% full-scale |
| Enclosure | IP68 with bellows / rod boot |
| Output | 4–20 mA, RS-485 Modbus, or 0–10 V |
6.2.4 Tilt / Inclinometers
| Parameter | Specification |
|---|
| Type | MEMS electrolytic or servo |
| Range | ±15° (biaxial) |
| Resolution | ≤ 0.001° (3.6 arc-seconds) |
| Temperature Compensation | Built-in, −20 to +70 °C |
| Output | RS-485 (Modbus RTU) or 4–20 mA |
6.2.5 Temperature Sensors
| Parameter | Specification |
|---|
| Type | Pt100 (Class A per IEC 60751) or thermistor (NTC 10 kΩ) |
| Range | −30 to +80 °C |
| Accuracy | ±0.15 °C (Pt100 Class A) |
| Placement | Ambient (shaded, ventilated), deck surface, soffit, inside box girder, at least
3 depths in concrete cross-section for thermal gradient |
6.2.6 Corrosion Sensors
| Parameter | Specification |
|---|
| Type | Half-cell potential probes, linear polarisation resistance (LPR), electrical resistivity |
| Measured Parameter | Corrosion potential (mV vs. Cu/CuSO&sb4;), corrosion rate (µm/year),
concrete resistivity (kΩ-cm) |
| Threshold (Alert) | Potential < −350 mV; Resistivity < 10 kΩ-cm;
Corrosion rate > 10 µm/year |
6.2.7 Scour Monitoring
| Parameter | Specification |
|---|
| Technology | Sonar (single/multi-beam), float-out device, or time-domain reflectometry (TDR) |
| Range | 0–20 m below riverbed |
| Accuracy | ±0.3 m (sonar) |
| Reporting Interval | Continuous during monsoon; hourly otherwise |
6.2.8 GNSS / Geodetic Monitoring
| Parameter | Specification |
|---|
| Type | Multi-constellation (GPS + GLONASS + NavIC + Galileo) L1/L2 |
| Horizontal Accuracy | ±5 mm + 1 ppm (static, post-processed) |
| Vertical Accuracy | ±8 mm + 1 ppm |
| Update Rate | 1 Hz (real-time); 20 Hz for dynamic monitoring |
| Reference Station | One stable reference within 5 km of bridge |
6.2.9 Weather Station
| Parameter | Specification |
|---|
| Wind Speed | Ultrasonic anemometer: 0–75 m/s, ±0.2 m/s accuracy, gust to 3 s |
| Wind Direction | 0–360°, ±3° |
| Air Temperature | −30 to +70 °C, ±0.1 °C |
| Relative Humidity | 0–100% RH, ±2% |
| Barometric Pressure | 300–1100 hPa, ±0.5 hPa |
| Rain Gauge | Tipping bucket: 0.2 mm resolution, 0–500 mm/h |
| Solar Radiation | Pyranometer: 0–2000 W/m², ISO 9060 Class B |
6.2.10 CCTV / Traffic Camera
One IP-based PTZ camera (minimum 4 MP, 30× optical zoom, IR night vision) at each bridge approach
and, for Level-3, one overlooking the deck. ONVIF Profile S compliant. Video streamed to the SHM
dashboard and archived for 30 days on a local NVR.
6.2.11 Weigh-in-Motion (WIM)
For Level-3 bridges, a bridge WIM (BWIM) system shall be integrated. Piezoelectric quartz sensors or
bending-plate sensors embedded in the approach pavement, capable of:
- Axle detection at 5–120 km/h
- Gross vehicle weight accuracy ±5%
- Single axle weight accuracy ±10%
- Classification per IRC vehicle classes + ASTM E1318 COST-323 Class B(10)
- Automatic overload alert when detected axle exceeds 1.5× legal limit
7. Data Acquisition, Transmission & Storage
7.1 Data Acquisition System (DAQ)
| Parameter | Specification |
|---|
| Architecture | Distributed — local DAQ nodes near sensor clusters connected via fibre-optic
backbone to a central server in the site control room |
| ADC Resolution | 24-bit sigma-delta per channel |
| Sampling Rate | 100 S/s (static), 1 kS/s (dynamic) per channel, simultaneously sampled |
| Anti-Aliasing Filter | Butterworth, 8-pole, cut-off at 40% of sampling rate |
| Time Synchronisation | GPS/GNSS-disciplined NTP or IEEE 1588 PTP; all channels time-stamped
to ±1 ms accuracy |
| Local Storage | Minimum 1 TB SSD per DAQ node — ring buffer for 90 days of raw data |
| Power Supply | 230 VAC ±15%, 50 Hz with UPS (4 hr battery);
optional solar + battery for remote sites |
| Environmental | NEMA 4X / IP66 enclosure; forced ventilation with filter;
internal temperature and humidity monitor |
| Surge Protection | All signal and power lines: SPD per IEC 61643-11, Class I+II |
| Self-Diagnostics | Watchdog timer; automatic reboot on lock-up; sensor health (open/short/excitation);
daily health report to central server |
7.2 Communication Backbone
| Link | Technology |
|---|
| DAQ to Central Server | Single-mode fibre (G.652.D), Gigabit Ethernet, redundant ring topology
with < 10 ms failover |
| Central Server to Cloud | 4G/LTE cellular router with automatic failover to 5G or VSAT;
minimum 50 Mbps uplink |
| Wireless Sensors (if any) | IEEE 802.15.4 (Zigbee) or LoRaWAN 868 MHz with AES-128 encryption;
range ≥ 500 m line-of-sight |
7.3 On-Site Server & Cloud Architecture
- On-Site Server: Industrial-grade rack server, dual Xeon or EPYC, 64 GB RAM, RAID-5 (4 × 4 TB HDD),
running Linux (RHEL / Ubuntu LTS). Hosts the real-time data ingestion, local database (TimescaleDB or
InfluxDB), and local dashboard. All data replicated to cloud within 60 seconds.
- Cloud Platform: Deployed on MeitY-empanelled cloud (NIC cloud, or commercial provider
with data centre in India). PostgreSQL/TimescaleDB for long-term archive. REST API for integration
with NHAI Bridge Management System (BMS).
- Data Retention:
- Raw dynamic data (1 kS/s): 30 days locally, 1 year in cloud (summary only after 30 days)
- 10-minute statistics (mean, max, min, std): 10 years
- Hourly statistics: retained for life of structure
- Event / alarm data: retained permanently
- CCTV footage: 30 days rolling
7.4 Data Security
- All data in transit encrypted via TLS 1.3
- VPN tunnel (IPsec) between site server and cloud
- Role-based access control (RBAC) with Aadhaar-linked or OTP-based 2FA
- Audit log of all user access and configuration changes
- Compliance with IT Act 2000 and MeitY data localisation requirements
8. Data Processing, Analytics & Threshold Alerts
8.1 Real-Time Processing Pipeline
- Ingestion: MQTT or Kafka-based stream from DAQ nodes;
- Validation: Range check, rate-of-change check, flat-line detection, spike removal;
- Unit Conversion: Raw counts → engineering units using calibration coefficients;
- Temperature Compensation: Apply thermal correction to strain and displacement readings
using co-located temperature sensors;
- Statistical Aggregation: Compute 10-minute window statistics (mean, max, min,
standard deviation, peak-to-peak);
- Threshold Comparison: Compare against predefined alert thresholds (Section 8.3);
- Storage: Time-series database; trigger event records if threshold exceeded.
8.2 Modal Analysis (Level-2 & Level-3)
The SHM software shall perform automated Operational Modal Analysis (OMA) at least once per day
(or on-demand) using Stochastic Subspace Identification (SSI-COV or SSI-DATA):
- Extract first 10–20 global modes depending on bridge complexity;
- Track natural frequencies, damping ratios, and Mode Assurance Criterion (MAC);
- Alert if any natural frequency shifts by > 10% from baseline (temperature-corrected);
- Alert if MAC value drops below 0.90 between successive analyses;
- Use modal data for FE model updating every 6 months.
8.3 Alert Thresholds & Alarm Protocol
A three-tier alarm system shall be implemented:
| Tier | Name | Trigger Condition | Response Time | Recipients |
|---|
| I |
Advisory (Blue) |
Parameter exceeds 80% of design limit, or 2σ from baseline |
Within 4 hours |
Dashboard notification; daily report |
| II |
Warning (Amber) |
Parameter exceeds 95% of design limit, or 3σ from baseline,
or sustained trend toward limit |
Within 30 minutes |
SMS + email to project engineer, concessionaire |
| III |
Critical (Red) |
Parameter exceeds design limit, or rate of change is sudden
(> 5σ event), or seismic acceleration exceeds
0.05 g (Zone IV/V trigger) |
Within 5 minutes |
SMS + voice call to project director, NHAI regional officer,
emergency protocol activation |
| Default Thresholds for Common Parameters |
|---|
| Parameter | Advisory (Blue) | Critical (Red) |
|---|
| Mid-span Deflection | > L/1000 | > L/800 |
| Concrete Compressive Strain | > 500 µε | > 1000 µε |
| Steel Tensile Strain | > 800 µε | > 1500 µε |
| Acceleration (peak) | > 0.5 m/s² | > 2.0 m/s² |
| Bearing Displacement | > 80% of design travel | > 95% of design travel |
| Tilt at Pier/Pylon | > 0.1° | > 0.3° |
| Scour Depth | > 50% of design scour depth | > 80% of design scour depth |
| Corrosion Potential | < −250 mV | < −350 mV |
| Wind Speed (10-min mean) | > 20 m/s | > 36 m/s (cyclone warning) |
| Rainfall Intensity | > 50 mm/h | > 100 mm/h |
Note: Thresholds presented are default values. The detailed design consultant shall
derive project-specific thresholds from the structural analysis and FE model. Alarm escalation
matrix and contact directory shall be maintained current at all times.
8.4 Dashboard & Visualisation
The SHM system shall include a web-based dashboard (mobile-responsive) providing:
- GIS-based map of all monitored bridges with colour-coded status;
- Real-time strip charts of all sensor channels with configurable time windows;
- 3D view of the bridge model with sensor locations overlaid and live colour-mapped values;
- Modal animation for the latest OMA results;
- Trend analysis: weekly, monthly, annual comparisons;
- Automatic PDF report generation (daily, weekly, monthly, and post-event);
- REST API for integration with NHAI BMS and third-party platforms;
- Role-based dashboards: Executive (summary KPIs), Engineer (technical detail),
Maintenance (condition indices).
9. Installation, Commissioning & Calibration
9.1 Pre-Installation Requirements
- Detailed SHM Design Report including: sensor location drawings, cable routing diagrams,
junction box locations, power budget, network topology, and integration test plan.
- Baseline FE model of the bridge (as-built) verified against construction records.
- Approval of installation methodology from the Engineer / Independent Engineer.
- Factory Acceptance Test (FAT) report for all sensors and DAQ hardware.
9.2 Sensor Installation
- Embedded Sensors: Installed during construction at pre-defined locations.
Cables routed through conduits to nearest junction box. All conduits sloped to drain.
- Surface-Mounted Sensors: Steel surfaces — grind to bright metal, epoxy adhesive
or spot-weld mounting base. Concrete surfaces — grind smooth, epoxy mounting base with
anchor bolts. All surfaces primed and sealed.
- Cable Routing: All cables in galvanised steel conduit (ISI-marked) or
HDPE duct; minimum 50 mm separation from power cables. Fibre optic in separate duct.
Cable tags at every 5 m and at both ends with unique ID.
- Junction Boxes: Stainless steel 304 (minimum 1.6 mm thick), IP68,
with desiccant cartridge, cable glands, internal DIN rail with surge protection devices,
and a unique QR-coded identifier.
- Lightning Protection: Air termination rods at bridge high points;
down-conductors bonded to bridge reinforcement; equipotential bonding of all SHM enclosures;
SPDs at every junction box. Earth resistance < 10 Ω per IS 3043.
9.3 Commissioning Tests
| Test | Method | Acceptance Criteria |
|---|
| Channel Continuity |
Inject known signal at sensor; verify at DAQ |
Signal within ±1% of injected value |
| Ambient Vibration Test |
Record 1 hour of ambient data; perform OMA |
At least first 5 modes identified with MAC > 0.95
(auto-MAC diagonal) |
| Controlled Load Test |
Known-weight truck (calibrated) at defined positions;
compare measured strain/deflection with FE prediction |
Measured vs. predicted within ±15% |
| Communication Test |
Verify end-to-end latency from sensor to cloud dashboard |
< 10 seconds (static channels), < 60 seconds
(dynamic/event data) |
| Alarm Test |
Simulate threshold breach by injecting synthetic data |
SMS/email delivered within specified response time |
| UPS Endurance Test |
Disconnect mains; verify system operation on battery |
Minimum 4 hours continuous operation |
| Failover Test |
Break primary fibre link; verify redundant path auto-switch |
Data gap < 10 seconds |
9.4 Baseline & Acceptable Range
Following commissioning, the system shall operate in baseline-acquisition mode for
90 days. During this period, no alerts shall be triggered (except self-diagnostics).
At the end of the baseline period, the statistical baseline (mean, standard deviation,
diurnal/seasonal envelopes) for each sensor shall be computed, reviewed, and frozen as the
reference. Thresholds shall be adjusted if the baseline reveals site-specific offsets.
10. Operation, Maintenance & Lifecycle Management
10.1 Warranty
- Sensors: 5 years from commissioning for surface-mounted;
10 years for embedded (manufacturer warranty).
- DAQ Hardware: 3 years.
- Software: 2 years with bug fixes and security patches.
10.2 Operations & Maintenance (O&M) Contract
For DBFOT / Annuity / HAM projects, the SHM O&M shall be included in the concession period.
For EPC projects, a separate 5-year O&M contract. Minimum requirements:
| Activity | Frequency | Responsibility |
|---|
| Sensor health check (diagnostics) | Daily (automated); weekly (manual review) | System integrator |
| DAQ / server health check | Daily automated report | System integrator |
| Field inspection of enclosures, cables, SPDs | Monthly | O&M contractor |
| Sensor recalibration (critical channels) | 12-monthly | System integrator |
| Sensor recalibration (all channels) | 24-monthly | NABL lab / manufacturer |
| Database backup verification | Monthly | System integrator |
| Software update / security patch | As released by vendor | System integrator |
| FE model update using SHM data | 6-monthly | Design consultant |
| System audit (third-party) | Annual | Independent engineer |
| OMA re-baseline | Annually (post-monsoon) | System integrator |
10.3 Data Ownership & Handover
All SHM data collected during the concession or O&M period is the property of the
Authority (NHAI / MORTH / State PWD). At the end of the contract term, the contractor
shall hand over:
- Complete raw and processed data archive (on HDD/SSD + cloud export);
- All calibration certificates;
- As-maintained drawings of the SHM system (sensor locations, cable routes, IP addresses);
- Source code or admin credentials for any proprietary analytics software;
- Training for Authority personnel (minimum 40 man-hours).
10.4 Sensor Replacement Protocol
- Failed sensor identified via diagnostics or during calibration;
- Replacement sensor of identical (or approved equivalent) specification procured;
- Replacement sensor calibrated at NABL-accredited lab;
- Installed at exactly the same location; cross-calibrated against adjacent functioning channel;
- Re-baseline period of 30 days before data is merged into long-term trend;
- Non-conformance report issued if MTBF falls below specified value.
11. Reporting, Compliance & Documentation
11.1 Automated Reports
| Report | Frequency | Content |
|---|
| Daily Health Summary | Daily, 08:00 IST | Sensor uptime, max/min values, any Tier-I alerts, DAQ status |
| Weekly Report | Every Monday | Trend plots, alert summary, maintenance actions, upcoming calibrations |
| Monthly Report | 1st of each month | Statistics, OMA results, condition indices, comparison with previous months,
traffic summary (WIM), consumption of consumables |
| Annual Structural Report | Annual | Full structural assessment, modal parameter evolution, FE model update
summary, remaining fatigue life estimate (if applicable), condition rating per IRC:SP:35 |
| Post-Event Report | Within 72 hours of any Red-tier event | Event timeline, peak parameter values, before/after modal comparison,
recommended inspection actions, immediate safety assessment |
11.2 Inspection Integration (IRC:SP:35)
SHM condition-based ratings (CBR) shall supplement visual inspection ratings. The SHM system
shall compute a quantitative condition index (0–100) for the following components:
- Superstructure (deflection, strain, modal parameters);
- Substructure (tilt, scour, settlement);
- Bearings & Expansion Joints (displacement, temperature correlation);
- Stay Cables / Hangers (force variability, corrosion);
- Deck & Wearing Course (from traffic camera + WIM overload count).
These component indices are weighted and combined into an overall Bridge Health Index (BHI),
which shall be stored in the NHAI Bridge Management System.
11.3 Compliance Checklist
| Compliance Item | Evidence |
|---|
| SHM design approved by Independent Engineer | Approval letter |
| All sensors calibrated (NABL traceable) | Calibration certificates |
| Commissioning tests passed | Signed test reports |
| 90-day baseline established | Baseline report |
| Dashboard accessible to Authority | URL + admin credentials deposited |
| Alarm protocol tested end-to-end | Test log with timestamps |
| Cloud data residency in India | Cloud provider certificate |
| O&M plan submitted and approved | Approved O&M manual |
12. Bid Evaluation & Vendor Qualification
12.1 Eligibility Criteria for SHM System Integrator
| Criterion | Requirement |
|---|
| Experience | Minimum 5 years in SHM instrumentation; at least 3 completed projects on
major bridges (span ≥ 60 m) in India or similar tropical/developing country |
| Financial | Average annual turnover ≥ INR 20 crore in instrumentation / SHM works
over last 3 financial years |
| Technical Personnel | Minimum 2 instrumentation engineers (M.Tech/ME in Structural/Civil),
2 electronics/DAQ engineers, 1 structural analyst with FE modelling experience |
| Certification | ISO 9001:2015; ISO/IEC 17025 (NABL) for in-house calibration or
tie-up with NABL lab |
| Past Performance | No blacklisting or contract termination by any government agency
in India in the last 3 years |
12.2 Bid Evaluation Criteria
| Parameter | Maximum Points |
|---|
| Technical proposal (sensor selection, redundancy, topology) | 30 |
| Software platform (dashboard, analytics, API, mobile app) | 20 |
| Experience on similar bridges in India | 15 |
| O&M plan and local support capability | 15 |
| Innovation (digital twin, AI/ML predictive analytics) | 10 |
| Price bid (financial) | 10 |
| Total | 100 |
Qualifying technical score: Minimum 70/90 (excluding price). Financial bid opened
only for technically qualified bidders. QCBS (Quality and Cost-Based Selection) method recommended
per NHAI procurement guidelines.
13. Annexures
Annexure A — Sample Sensor Schedule for a Cable-Stayed Bridge
Example: 3-span cable-stayed bridge, main span 250 m, two pylons, 96 stay cables.
| Sensor Type | Quantity | Location |
|---|
| Accelerometer (triaxial, force-balance) | 24 | Deck at L/8 spacings; pylon top × 2 |
| VW Strain Gauge (embedded) | 48 | Deck soffit at L/4, L/2, 3L/4; pylon base |
| VW Strain Gauge (surface) | 96 | Representative stay cables (every 4th cable) |
| Accelerometer on Cable (uniaxial) | 24 | Selected stay cables for tension measurement |
| Displacement Sensor | 8 | Expansion joints × 4; pylon-deck connection |
| Tilt Meter (biaxial) | 6 | Pylon top × 2; pier base × 4 |
| Temperature Sensor (Pt100) | 36 | Deck cross-section × 3 locations × 4 depths; ambient |
| Anemometer (ultrasonic 2D) | 2 | Pylon top; deck mid-span |
| GNSS Rover + Base | 3 + 1 | Deck at L/2 and each pylon top; base on stable ground |
| Corrosion Probe | 12 | Pylon base; deck edge zones |
| Scour Sonar | 4 | Each pier in river |
| Weather Station | 1 | Deck level |
| IP Camera (PTZ) | 4 | Approach × 2; deck overview × 2 |
| BWIM System | 1 | Approach lane level |
| Strong-Motion Accelerograph | 2 | Pylon base; free-field |
Annexure B — Abbreviations
| Abbreviation | Full Form |
|---|
| AASHTO | American Association of State Highway and Transportation Officials |
| BIS | Bureau of Indian Standards |
| BMS | Bridge Management System |
| BWIM | Bridge Weigh-in-Motion |
| CCTV | Closed-Circuit Television |
| CBR | Condition-Based Rating |
| DAQ | Data Acquisition |
| FBG | Fibre Bragg Grating |
| FE | Finite Element |
| GNSS | Global Navigation Satellite System |
| IEPE | Integrated Electronics Piezo-Electric |
| IRC | Indian Roads Congress |
| LVDT | Linear Variable Differential Transformer |
| MAC | Modal Assurance Criterion |
| MEMS | Micro-Electro-Mechanical Systems |
| MORTH | Ministry of Road Transport & Highways |
| MTBF | Mean Time Between Failures |
| NABL | National Accreditation Board for Testing and Calibration Laboratories |
| NHAI | National Highways Authority of India |
| OMA | Operational Modal Analysis |
| PSC | Prestressed Concrete |
| RCC | Reinforced Cement Concrete |
| SHM | Structural Health Monitoring |
| SPD | Surge Protection Device |
| VW | Vibrating Wire |
| WIM | Weigh-in-Motion |